JP2002204276A - Data communication system, method for controlling power supply and power supply receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem that it is difficult to optimize power reception balance between devices in a data communication system based on an IEEE1394 standard. SOLUTION: In this system in which a power supply, device is connected to a power receiving device by a serial bus capable of supplying power source, the power receiving device issues request information showing request power supply (S2701), and when the power supply request is appropriate for the power supply device, the requested power supply is performed by the power supply device in an operation mode (S2702, S2703 and S2714). On the other hand, when the power supply request is not appropriate, the power supply request is modified to make any other operation mode performable and the request information is reissued (S2702, S2704 and S2705).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a data communication system, a power control method therefor, and a power receiving apparatus, for example, a data communication system for controlling power supply between devices connected by a serial bus based on the IEEE 1394 standard, and a data communication system therefor. The present invention relates to a power control method and a power receiving device.

[0002]

2. Description of the Related Art IEEE 1394-1995. a interface (hereinafter referred to as 1394)
In this case, the power management is also specified. For example, the definition of the power requesting side and the power supplying side is divided into three stages, and the matching of each stage is controlled by a bus manager which performs serial bus management only in this power range.

[0003]

However, in the above-mentioned conventional 1394 serial bus, since the power range that can be supplied and requested is limited to three stages, fine power control cannot be performed. Therefore, for example, there are problems that it is not possible to cope with a case where the power demand exceeds the power supply side, and it is not possible to effectively use the power supply side capability.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and a data communication system and a power control method for optimizing a power supply / reception balance between devices connected by a serial bus based on the IEEE 1394 standard. And a power receiving device.

[0005]

As a means for achieving the above object, a data communication system of the present invention has the following arrangement.

That is, a data communication system in which a power supply device and a power receiving device are connected by a serial bus capable of supplying power, wherein the power receiving device issues request information indicating a required amount of power. Acquiring means for acquiring supply information indicating the suppliable power amount in the power supply device, and when the required power amount indicated by the request information is appropriate for the suppliable power amount indicated by the supply information, Power receiving means for receiving power based on the required power amount from the power supply device, and operating means for selectively executing a plurality of operation modes according to the power amount received by the power receiving means;
The issuing means, when the required power amount indicated by the issued request information is not appropriate for the suppliable power amount indicated by the supply information, It is characterized in that the operation mode is changed to be executable and the request information is reissued.

[0007] For example, the issuing means is characterized in that the required power is reduced stepwise and the required information is reissued.

In a data communication system, a first and a second device using a battery as a drive source are connected to each other by a serial bus capable of supplying power, wherein the first device has a remaining battery capacity. Issuing means for issuing, to the second device, request information indicating a required power amount in a plurality of stages when the power amount is equal to or less than a predetermined amount; And power receiving means for receiving, from the second device, power based on the required amount of power at the permitted stage when power supply is permitted by the answer, and The required power amount at each stage is a required power amount corresponding to each of a plurality of operation modes in the first device.

For example, the serial bus is an IEEE1
It is a bus conforming to or conforming to the 394 standard.

In a data communication system, a power supply device and a power reception device are connected by a serial bus capable of supplying power, wherein the power reception device issues request information indicating a required amount of power. An acquisition unit for acquiring supply information indicating an amount of power that can be supplied by the power supply device; a power receiving unit for receiving power from the power supply device; and a plurality of operation modes in which the amount of power required for operation is different. Operating means, and the issuing means, when the requested power amount indicated by the issued request information is not appropriate for the suppliable power amount indicated by the supply information, the requested power amount It is characterized in that any one of the operation modes in the operation means is changed to be executable.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment according to the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a diagram showing a general configuration example of a system to which the present invention is applied, in which a digital camera 101 and a printer 102 are connected using a 1394 serial bus. Therefore, an outline of the 1394 serial bus will be described in advance. The digital camera 101 consumes relatively little power as an image input device, and
Has power supply capability.

<Description of 1394 Serial Bus> With the advent of home digital VTRs and digital video discs (DVD), video data and audio data
It is necessary to transfer data with a large amount of information in real time, such as "AV data". A
In order to transfer V data to a PC or other digital devices in real time, an interface having a high-speed data transfer capability is required. An interface developed from such a viewpoint is the 1394 serial bus.

The details of the IEEE 1394-1995 standard (hereinafter, IEEE 1394 standard) are described in 199
On August 30, 2006, the IEEE (The Institute of Electr)
icaland Electronics Engineers, Inc.) published by IEEE Standard for a High Performance Serial Bus
It is described in.

(1) Overview FIG. 2 shows an example of a communication system (hereinafter, a 1394 network) constituted by nodes having a 1394 serial bus. The 1394 network constitutes a bus network capable of communicating serial data.

In FIG. 2, each of the nodes A to H is an IEEE
They are connected via a communication cable conforming to the E1394 standard. These nodes A to H are, for example, PC (Per
sonal Computer), Digital VTR (Video Tape Recorde)
r), electronic equipment such as a DVD (Digital Video Disc) player, a digital camera, a hard disk, and a monitor.

The connection method of the 1394 network corresponds to a daisy chain method and a node branch method.
A highly flexible connection is possible. In the 1394 network, for example, existing devices are deleted, new devices are added, and the power of the existing devices is turned on / off.
In such a case, the bus is automatically reset. By performing the bus reset, the 1394 network can automatically recognize a new connection configuration and assign ID information to each device. With this function, the 1394 network can always recognize the connection configuration of the network.

The 1394 network has a function of relaying data transferred from another device. With this function, all devices can grasp the operation status of the bus.

[0019] The 1394 network is provided by Plug &
It has a function called Play. With this function, the connected device can be automatically recognized only by connecting without turning off the power of all devices.

The 1394 network is 100/2
It corresponds to a data transfer rate of 00/400 Mbps. A device having a higher data transfer speed can support a lower data transfer speed, and thus can connect devices corresponding to different data transfer speeds.

Further, the 1394 network supports two different data transfer methods (ie, asynchronous transfer mode and synchronous transfer mode).

The asynchronous transfer mode is effective when transferring data that is required to be transferred asynchronously as needed (ie, control signals, file data, etc.). In addition, the synchronous (Isochronous) transfer mode is effective when transferring data (that is, video data, audio data, and the like) required to continuously transfer a predetermined amount of data at a constant data rate.

The asynchronous transfer mode and the synchronous transfer mode are as follows.
It is possible to mix them within each communication cycle (usually one cycle is 125 μS). Each transfer mode is executed after transfer of a cycle start packet (hereinafter, CSP) indicating the start of a cycle.

In each communication cycle period, the priority of the synchronous transfer mode is set higher than that of the asynchronous transfer mode. The transfer band in the synchronous transfer mode is guaranteed within each communication cycle.

(2) Architecture Next, the components of the 1394 serial bus will be described with reference to FIG.

The 1394 serial bus is functionally composed of a plurality of layers (layers). In FIG. 3, 1
The 394 serial bus is connected to a 1394 serial bus of another node via a communication cable 301 conforming to the IEEE 1394 standard. The 1394 serial bus has one or more communication ports 302,
02 is connected to the physical layer 303 included in the hardware unit.

In FIG. 3, the hardware section is composed of a physical layer 303 and a link layer 304. The physical layer 303 includes a physical / electrical interface with another node, detection of a bus reset and processing accompanying the same, encoding / decoding of input / output signals,
Arbitrates the right to use the bus. Also, the link layer 304
Performs generation and transmission / reception of communication packets, control of a cycle timer, and the like.

In FIG. 3, the firmware section
It includes a transaction layer 305 and a serial bus management 306. The transaction layer 305 manages the asynchronous transfer mode and provides various transactions (read, write, lock). The serial bus management 306 controls the own node based on the CSR architecture described later,
It provides functions for managing the connection state of the own node, managing ID information of the own node, and managing resources of the serial bus network.

As described above, the hardware section and the firmware section substantially constitute a 1394 serial bus, and the basic configuration thereof is defined by the IEEE 1394 standard.

The application layer 307 included in the software section differs depending on the application software used, and controls how data is communicated on the network. For example, digital VTR
Is defined by a communication protocol such as the AV / C protocol.

(2-1) Link Layer 304 FIG. 4 is a diagram showing services that the link layer 304 can provide. In FIG. 4, the link layer 304
Provides the following four services. That is, a link request for requesting the responding node to transfer a predetermined packet.
(LK_DATA.request), a link notification (LK_DATA.indication) for notifying the response node of reception of a predetermined packet, a link response (LK_DATA.response) indicating that an acknowledgment has been received from the response node, and an acknowledgment from the request node. Link confirmation to confirm (LK_DATA.confirmation)
It is. The link response (LK_DATA.response) does not exist in the case of broadcast communication and transfer of a synchronization packet.

The link layer 304 realizes the above-mentioned two types of transfer systems, that is, the asynchronous transfer mode and the synchronous transfer mode, based on the above-mentioned services.

(2-2) Transaction Layer 30
5 is a diagram showing services that can be provided by the transaction layer 305. In FIG. 5, the transaction layer 305 provides the following four services. That is, a transaction request (TR_DATA.reques
t), a transaction notification (TR_DATA.indicatio
n), a transaction response (TR_DATA.response) indicating that status information (including data in the case of write or lock) has been received from the responding node, and a transaction confirmation (TR_DATA.confi) confirming status information from the requesting node
rmation).

The transaction layer 305 includes:
Asynchronous transfer is managed based on the above service, and the following 3
A type of transaction is realized, that is, a read transaction, a write transaction, and a lock transaction.

In a read transaction, a requesting node reads information stored at a specific address of a responding node.

In a write transaction, a requesting node writes predetermined information to a specific address of a responding node.

In the lock transaction, the requesting node transfers reference data and update data to the responding node, compares the information of the specific address of the responding node with the reference data, and specifies the specific address according to the comparison result. Is updated to the update data.

(2-3) Serial Bus Management 306 The serial bus management 306 is, specifically,
The following three functions can be provided. The three functions are a node control, an isochronous resource manager (hereinafter, IRM), and a bus manager.

The node control provides a function of managing the above-described layers and managing asynchronous transfer executed with another node.

The IRM provides a function for managing a synchronous transfer performed between another node. Specifically, it manages information necessary for assigning a transfer bandwidth and a channel number, and provides this information to other nodes.

The IRM exists only on the local bus,
Each time the bus is reset, it is dynamically selected from other candidates (nodes having an IRM function).

The IRM may provide some of the functions (such as connection configuration management, power supply management, and speed information management) that can be provided by a bus manager described later.

The bus manager has an IRM function and provides a more advanced bus management function than the IRM. More specifically, more advanced power management (information on whether or not power supply is possible via a communication cable, whether or not power supply is necessary for each node, etc.), more advanced speed information Management (management of the maximum transfer rate between each node), management of a more advanced connection configuration (creation of a topology map), optimization of a bus based on the management information, and the like, and further transfer of the information to other nodes It has a function to provide.

The bus manager can provide a service for controlling the serial bus network to the application. Here, the service includes a serial bus control request (SB_CONTROL.request), a serial bus event control confirmation (SB_CONTROL.confirmation), a serial bus event notification (SB_CONTROL.indication), and the like.

SB_CONTROL.request is a service for requesting a bus reset by an application. SB_CONTR
OL.confirmation is a service for confirming SB_CONTROL.request to an application. SB_CONTROL.i
ndication is a service that notifies an application of an event that occurs asynchronously.

(3) Address designation FIG. 6 is a diagram for explaining an address space in the 1394 serial bus. The 1394 serial bus is IS
O / IEC 13213: CSR according to 1994 (Com
mand and Status Register)
It defines a 4-bit width address space.

In FIG. 6, the first 10-bit field 601 is used for an ID number for specifying a predetermined bus, and the next 6-bit field 602 is used for an ID number for specifying a predetermined device (node). Is done. The upper 16 bits are called “node ID”, and each node identifies another node by this node ID. Further, each node can perform communication in which the other party is identified using the node ID.

The remaining 48-bit field is
The address space (256 Mbyte structure) of each node is specified. 20-bit field 60 of them
3 designates a plurality of areas constituting the address space.

In the field 603, "0 to 0xF
The “FFFD” part is called a memory space. "0xF
The “FFFE” portion is called a private space, and is an address that can be freely used by each node. Also, "0xF
The “FFFE” portion is called a register space, and stores common information between nodes connected to the bus. Each node can manage communication between the nodes by using the information of the register space.

The last 28-bit field 604 is
Designate an address where common or unique information is stored in each node.

For example, in the register space, the first five
12 bytes are the core of the CSR architecture (CSR
Used for core) registers. FIG. 7 shows addresses and functions of information stored in the CSR core register. The offset in the figure is "0xFFFFF00000000"
It is a relative position from.

The next 512 bytes are used as a register for the serial bus.

FIG. 8 shows addresses and functions of information stored in the serial bus register. The offset in the figure is a relative position from “0xFFFFF0000200”.

The next 1024 bytes are used for the configuration ROM. The configuration ROM has a minimum format and a general format.
FFFF0000400 ”. FIG. 9 shows a configuration ROM of the minimum format. In FIG. 9, the vendor ID is a 24-bit numerical value uniquely assigned to each vendor by IEEE.

A general configuration R
The OM is shown in FIG. Referring to FIG.
D is stored in the Root Directory 1002. Bus
InfoBlock 1001 and Root Leaf 1005 have a node unique ID as unique ID information for identifying each node.
Can be held.

Here, the node unique ID is the manufacturer,
Regardless of the model, a unique ID that can specify one node is determined. The node unique ID is composed of 64 bits, the upper 24 bits indicate the above-described vendor ID, and the lower 48 bits are information that can be freely set by a manufacturer that manufactures each node (for example,
Node serial number). The node unique ID is used, for example, when a specific node is continuously recognized before and after a bus reset. In FIG. 10, the Root Directory 1002 can hold information on basic functions of the node. Detailed function information is stored in a subdirectory (Unit Directories 1004) offset from the Root Directory 1002. In the Unit Directories 1004, for example, information on software units supported by the node is stored. In other words, information on a data transfer protocol for performing data communication between nodes, a command set for defining a predetermined communication procedure, and the like are held.

In FIG. 10, Node Dependent Inf
o Directory 1003 can hold device-specific information. Node Dependent Info Director
y1003 is offset by Root Directory 1002.

Further, in FIG. 10, Vendor Dependent
Information 1006 can hold information unique to the vendor that manufactures or sells the node.

The remaining area is called a unit space, and specifies an address in which information unique to each node, for example, identification information (company name, model name, etc.) of each device, use conditions, and the like are stored. FIG. 11 shows addresses and functions of information stored in the serial bus device register in the unit space. The offset in the figure is a relative position from “0xFFFFF0000800”.

Generally, when it is desired to simplify the design of a heterogeneous bus system, each node should use only the first 2048 bytes of the register space. That is, CS
R core register, serial bus register, configuration ROM, first 2048 of unit space
It is desirable that the total number of bytes is 4096 bytes.

(4) Configuration of Communication Cable FIG. 12 is a sectional view of a communication cable conforming to the IEEE 1394 standard.

The communication cable is composed of two twisted pair signal lines and a power supply line. By providing the power supply line, the 1394 serial bus can supply power to a device whose main power is turned off, a device whose power is reduced due to a failure, and the like. The voltage of the power supply flowing in the power supply line is 8 to 40 V, and the current is the maximum current DC1.5.
A is specified.

The DS-L is connected to the two twisted pair signal lines.
An information signal is transmitted by an ink (Data / Strobe Link) method. FIG. 13 is a diagram illustrating the DS-Link system.

The DS-Link system is suitable for high-speed serial data communication, and its configuration requires two pairs of twisted pairs. One twisted pair carries a data signal, and the other twisted pair sends a strobe signal. The receiving side can reproduce the clock by taking the exclusive OR of the data signal and the strobe signal received from the two pairs of signal lines.

By using the DS-Link system, the 1394 serial bus has the following advantages, for example. Higher transfer efficiency than other serial data transfer methods. No PLL circuit is required, and the controller L
The circuit size of the SI can be reduced. Since there is no need to send information indicating the idle state, the transceiver circuit can be easily put into the sleep state, and power consumption can be reduced.

(5) Bus Reset The 1394 serial bus of each node can automatically detect that a change has occurred in the network connection configuration. In this case, the 1394 network performs a process called a bus reset according to the following procedure. The change in the connection configuration can be detected by a change in the bias voltage applied to the communication port of each node. A node that detects a change in the network connection configuration (for example, an increase or decrease in the number of nodes due to insertion / removal of a node, power ON / OFF of a node, or the like) or a node that needs to recognize a new connection configuration is connected via the 1394 serial bus. And transmits a bus reset signal on the bus.

The node 13 that has received the bus reset signal
The 94 serial bus transmits the occurrence of a bus reset to its own link layer 304 and transfers the bus reset signal to another node. The node that has received the bus reset signal clears the network connection configuration and the node ID assigned to each device that have been recognized so far. After all the nodes finally detect the bus reset signal, each node automatically performs initialization processing (that is, recognition of a new connection configuration and assignment of a new node ID) accompanying the bus reset.

The bus reset is activated by the application layer 307 directly issuing a command to the physical layer 303 under the control of the host, in addition to the activation caused by the change of the connection configuration as described above. It is also possible to make it.

When the bus reset is activated, the data transfer is temporarily suspended, and is resumed under a new network after the completion of the initialization process accompanying the bus reset.

(6) Sequence after Starting Bus Reset After starting the bus reset, the 1394 serial bus of each node automatically recognizes a new connection configuration and assigns a new node ID. Hereinafter, a basic sequence from the start of the bus reset to the node ID assignment processing will be described with reference to FIGS.

FIG. 14 is a diagram for explaining a state after the bus reset is activated in the 1394 network of FIG.

In FIG. 14, node A has one communication port, node B has two communication ports, node C has two communication ports, node D has three communication ports, node E has one communication port, and node F has one communication port. It has one communication port. The communication port of each node is provided with a port number for identifying each port.

Hereinafter, the process from the start of the bus reset to the assignment of the node ID in FIG. 14 will be described with reference to the flowchart in FIG.

In FIG. 15, each of the nodes A to F constituting the 1394 network constantly monitors whether or not a bus reset has occurred (step S1501). When a bus reset signal is output from a node that has detected a change in the connection configuration, each node executes the following processing.

After the occurrence of the bus reset, each node declares a parent-child relationship between the respective communication ports (step S1502).

Each node repeats the process of step S1502 until the parent-child relationship between all nodes is determined (step S1503).

After the parent-child relationship between all nodes is determined,
The 1394 network determines a node that performs network arbitration, that is, a route (step S150).
4).

After the route is determined, the 1394
Each serial bus executes a task of automatically setting its own node ID (step S1505).

Until node IDs are set for all nodes, each node executes the processing of step S1505 according to a predetermined procedure (step S1506).

Finally, node IDs for all nodes
Is set, each node executes synchronous transfer or asynchronous transfer (step S1507).

At the same time as executing the processing in step S1507, the 1394 serial bus of each node monitors the occurrence of a bus reset again. If a bus reset has occurred, the processing after step S1501 is executed again.

According to the above procedure, the 1394 serial bus of each node can automatically recognize a new connection configuration and assign a new node ID every time a bus reset is activated.

(7) Determination of Parent-Child Relationship Next, referring to FIG. 16, step S15 shown in FIG.
02 (that is, the process of recognizing the parent-child relationship between the nodes) will be described in detail.

In FIG. 16, after the occurrence of the bus reset,
Each of the nodes A to F on the 1394 network confirms the connection state (connected or not connected) of the communication port provided therein (step S1601).

After confirming the connection state of the communication port, each node counts the number of communication ports (hereinafter, connection ports) connected to other nodes (step S160).
2).

If the result of the processing in step S1602 is that the number of connection ports is one, the node recognizes that it is a “leaf” (step S1603). Here, a leaf is a node connected to only one node.

The node serving as a leaf is called “Child” by the node connected to the connection port.
Is declared (step S1604). At this time, the leaf recognizes that the connection port is “parent port (communication port connected to the parent node)”. Here, the declaration of the parent-child relationship is first made between the leaf and the branch, which are the ends of the network, and then sequentially made between the branches. The parent-child relationship between the nodes is determined in order from the communication port that can make the declaration earlier. In addition, the communication port that is declared as a child between the nodes is recognized as a “parent port”, and the communication port that receives the declaration is a “child port (communication port connected to the child node)”. It is recognized that there is. For example, in FIG. 14, the nodes A, E, and F declare a parent-child relationship after recognizing that they are leaves. This allows
Child-parent between nodes AB, child-node between nodes E-D
It is determined as a child-parent between the parent and the node FD.

If the result of the processing in step S1602 is that the number of connection ports is two or more, the node recognizes itself as a "branch" (step S160).
5). Here, a branch is a node connected to two or more nodes.

The node serving as the branch receives the declaration of the parent-child relationship from the node of each connection port (step S1).
606). The connection port that has accepted the declaration is recognized as a “child port”.

After recognizing one connection port as a “child port”, the branch detects whether or not there are two or more connection ports for which a parent-child relationship has not yet been determined (that is, an undefined port) (step S1). S1607). As a result, if there are two or more undefined ports, the branch performs the operation of step S1606 again.

As a result of step S1607, if there is only one undefined port, the branch recognizes that the undefined port is the “parent port”, and sends a “own” to the node connected to that port. Is a child "(steps S1608 and S1609).

Here, the branch cannot declare itself as a child to other nodes until the number of remaining undefined ports becomes one. For example, in FIG. 14, nodes B, C, and D recognize that they are branches and accept a declaration from a leaf or another branch. After the parent-child relationship between DE and DF is determined, the node D declares the parent-child relationship to the node C. Node C, which has received the declaration from node D,
The parent-child relationship is declared to node B.

If there is no undefined port as a result of the processing in step S1608 (that is, if all the tangent ports of the branch have become parent ports), the branch itself must be a root. Is recognized (step S1610).

For example, in FIG. 14, a node B in which all of the connection ports are parent ports is recognized by another node as a route for mediating communication on the 1394 network. Here, although the node B is determined to be the root, if the timing of declaring the parent-child relationship of the node B is earlier than the timing of declaring the node C, another node may be the root. That is, depending on the timing of declaration, any node may be the root.
Therefore, even with the same network configuration, the same node does not always become the root.

By declaring the parent-child relationship of all connection ports in this manner, each node can recognize the connection configuration of the 1394 network as a hierarchical structure (tree structure) (step S1611). The above-mentioned parent node is higher in the hierarchical structure, and the child node is lower in the hierarchical structure.

(8) Assignment of Node ID FIG. 17 is a flowchart for explaining in detail the process of step S1505 shown in FIG. 15 (ie, the process of automatically assigning the node ID of each node). here,
The node ID is composed of a bus number and a node number. In this embodiment, it is assumed that each node is connected on the same bus, and that each node is assigned the same bus number.

In FIG. 17, the root gives the node ID setting permission to the communication port having the smallest number among the child ports to which the node whose node ID is not set is connected (step S1701).

In FIG. 17, after setting the node IDs of all the nodes connected to the child port with the smallest number, the root is set to the child port, and the same is applied to the next smallest child port. Is controlled. After the ID setting of all nodes finally connected to the child port is completed,
Set the node ID of the root itself. The node numbers included in the node ID are basically assigned as 0, 1, 2,... In the order of leaf and branch. Therefore, the route will have the highest node number.

In step S1701, the node that has obtained the setting permission determines whether or not there is a child port including the node whose node ID is to be set among its own child ports (step S1702).

If a child port including an unset node is detected in step S1702, the node that has obtained the above setting permission controls the node directly connected to the child port to give the setting permission. (Step S1703).

After the processing in step S1703, the node which has obtained the above setting permission has the node ID of its own child port.
It is determined whether or not there is a child port including a node for which is not set (step S1704). Here, step S1
If the existence of the child port including the unset node is detected after the process of 704, the node returns to step S170
Step 3 is executed.

Step S1702 or S1704
In step S1705, if no child port including an unset node is detected, the node that has obtained the setting permission sets its own node ID (step S1705).

The node that has set its own node ID broadcasts a self-ID packet containing information about its own node number, the connection state of the communication port, and the like (step S1706). In addition, broadcast is
This is to transfer a communication packet of a certain node to an unspecified number of nodes constituting the 1394 network.

Here, each node can recognize the node number assigned to each node by receiving the self ID packet, and can know the node number assigned to itself. For example, in FIG. 14, the root node B has the minimum port number “#”.
The permission of the node ID setting is given to the node A connected to the communication port of "1". The node A assigns its own node number “No. 0” and sets a node ID including a bus number and a node number for itself. Further, the node A broadcasts a self ID packet including the node number.

FIG. 18 shows a configuration example of a self ID packet. In FIG. 18, reference numeral 1801 denotes a field for storing the node number of the node that transmitted the self ID packet;
A field 802 stores information on transfer rates that can be supported, a field 1803 indicates a presence or absence of a bus management function (such as the presence or absence of a bus manager), and a field 1804 stores information on characteristics of power consumption and supply ( Pwr).

In FIG. 18, reference numeral 1805 denotes a field for storing information relating to the connection state of the communication port having the port number "# 0" (connected, unconnected, parent-child relationship of the communication port, etc.), and 1806 denotes the port number "#". A field for storing information (connection, non-connection, parent-child relationship of the communication port, etc.) relating to the connection state of the communication port of "1". Connection, parent-child relationship of communication ports, etc.). If the node transmitting the self ID packet has the ability to become a bus manager, the contender bit shown in the field 1803 is set to “1”, and if not, the contender bit is set to 0.

Here, the bus manager refers to the power management of the bus (whether or not power can be supplied via a communication cable, the power needs to be supplied) based on various information included in the self ID packet. Information on whether or not each node is managed), management of speed information (manage maximum transfer speed between nodes based on information on transfer speeds that can be supported by each node), management of topology map information The node has a function of managing the connection configuration of the network from the parent-child relationship information of the communication ports, optimizing the bus based on the topology map information, and providing the information to other nodes. With these functions, a node serving as a bus manager can perform bus management of the entire 1394 network.

After the processing in step S1706, the node ID
The node that has made the setting determines whether there is a parent node (step S1707). If there is a parent node, the parent node executes the processing of step S1702 and subsequent steps again. Then, permission is given to a node whose node ID has not been set yet.

If the parent node does not exist, it is determined that the node is the root itself. The root determines whether a node ID has been set for the nodes connected to all the child ports (step S1708).

If the ID setting process for all nodes is not completed in step S1708, the root grants ID setting permission to the child port having the smallest number among the child ports including the node (step S1708). S1
701). After that, the processing from step S1702 is executed.

When the ID setting processing for all nodes is completed, the root sets its own node ID (step S1709). After setting the node ID, the route broadcasts a self ID packet (step S1710).

By the above processing, the 1394 network can automatically assign a node ID to each node.

Here, if a plurality of nodes have the bus manager capability after the node ID setting process, the node with the largest node number becomes the bus manager. That is, if the route having the maximum node number in the network has a function that can be the bus manager, the route becomes the bus manager.

However, when the route does not have the function, the node having the next highest node number becomes the bus manager. Further, which node has become the bus manager can be grasped by checking the contender bit 1803 in the self ID packet broadcast by each node.

(9) Arbitration FIG. 19 is a diagram for explaining arbitration in the 1394 network shown in FIG.

In the 1394 network, arbitration (arbitration) of the right to use the bus is always performed prior to data transfer. The 1394 network is a logical bus network. By relaying a communication packet transferred from each node to another node, the same communication packet can be transferred to all nodes in the network.

Therefore, arbitration is necessary to prevent collision of communication packets. This allows only one node to transfer at a given time.

FIG. 19A is a diagram for explaining a case where the node B and the node F have issued a bus use request.

When arbitration starts, node B,
F issues a bus use request to each parent node. The parent node (ie, node C) that has received the request from node B relays its bus use right to its parent node (ie, node D). This request is finally delivered to the arbitrating route (node D).

The route receiving the bus use request determines which node uses the bus. This arbitration work can be performed only by the root node, and the node that wins the arbitration is given permission to use the bus.

FIG. 19B is a diagram showing that the request from the node F is permitted and the request from the node B is rejected.

The route sends a DP (Data prefix) packet to the node that has lost arbitration to notify that the node has been rejected. The rejected node waits for a bus use request until the next arbitration. By controlling arbitration as described above, 1
The 394 network can manage the right to use the bus.

(10) Communication cycle The synchronous transfer mode and the asynchronous transfer mode can be mixed in a time division manner in each communication cycle period. Here, the period of the communication cycle is usually 125 μS.

FIG. 20 is a diagram for explaining a case where the synchronous transfer mode and the asynchronous transfer mode are mixed in one communication cycle.

The synchronous transfer mode is executed prior to the asynchronous transfer mode. The reason is that after the cycle start packet, the idle period (subaction gap) required to start the asynchronous transfer is set to be longer than the idle period (Isochronous gap) required to start the synchronous transfer. That is because. Thereby, the synchronous transfer is executed prior to the asynchronous transfer.

In FIG. 20, at the start of each communication cycle, a cycle start packet (hereinafter referred to as CS
P) is transferred from a predetermined node. Each node can measure the same time as the other nodes by adjusting the time using the CSP.

(11) Synchronous transfer mode The synchronous transfer mode is a synchronous transfer system. The synchronous transfer mode can be executed for a predetermined period after the start of the communication cycle. The synchronous transfer mode is always executed every cycle in order to maintain real-time transfer.

The synchronous transfer mode is a transfer mode suitable for transferring data requiring real-time transfer, such as moving image data and audio data. The synchronous transfer mode is not a one-to-one communication as in the asynchronous transfer mode but a broadcast communication. That is, a packet transmitted from a certain node is uniformly transferred to all nodes on the network. Note that there is no ack (reply code for reception confirmation) in the synchronous transfer.

In FIG. 20, channel e (ch)
e), channel s (ch s), channel k (ch
k) indicates a period during which each node performs synchronous transfer. 139
In the 4-serial bus, different channel numbers are given to distinguish a plurality of different synchronous transfers. This enables synchronous transfer between a plurality of nodes. Here, the channel number does not specify the transmission destination, but merely gives a logical number for the data.

The isochronous gap shown in FIG. 20 indicates an idle state of the bus. After a certain period of time in the idle state, the node desiring the synchronous transfer determines that the bus can be used and executes arbitration.

Next, FIG. 21 shows a format of a communication packet transferred based on the synchronous transfer mode. Less than,
Communication packets transferred based on the synchronous transfer mode
It is called a synchronization packet.

In FIG. 21, the synchronization packet includes a header section 2101, a header CRC 2102, a data section 2103,
It consists of data CRC2104.

The header section 2101 has a data section 2103
A field 2105 for storing the data length of the synchronization packet, a field 2106 for storing the format information of the synchronization packet,
Field 21 for storing channel number of synchronization packet
07, a field 2108 for storing a transaction code (tcode) for identifying the format of the packet and processing to be executed, and a field 2109 for storing a synchronization code.

(12) Asynchronous Transfer Mode The asynchronous transfer mode is an asynchronous transfer system.

Asynchronous transfer can be performed after the end of the synchronous transfer period until the next communication cycle starts (that is, until the CSP of the next communication cycle is transferred).

In FIG. 20, the first sub-action
The gap (subaction gap) indicates an idle state of the bus. After this idle time reaches a certain value,
A node desiring asynchronous transfer determines that the bus can be used and executes arbitration.

The node which has obtained the right to use the bus by arbitration transfers the packet shown in FIG. 22 to a predetermined node. The node that has received this packet
ck (Return code for reception confirmation) or response packet ac
Return after k gap.

FIG. 22 is a diagram showing a format of a communication packet based on the asynchronous transfer mode. Hereinafter, a communication packet transferred based on the asynchronous transfer mode is referred to as an asynchronous packet.

In FIG. 22, an asynchronous packet includes a header section 2201, a header CRC 2202, and a data section 220.
3. Data CRC 2204.

In header section 2201, field 2
205 is the node ID of the destination node, field 2206 is the node ID of the source node, field 2207 is a label indicating a series of transactions, field 2208 is a code indicating the retransmission status, and field 2209 is A transaction code (tcode) for identifying the format of the packet and a process to be executed, a priority in a field 2210, a destination memory address in a field 2211, a data length of a data part in a field 2212, and a data length of a data part in a field 2213 The extended transaction code is stored.

Asynchronous transfer is one-to-one communication from a self-node to a partner node. The packet transferred from the transfer source node is distributed to each node in the network, but the address other than the address addressed to itself is ignored. Therefore, only the destination node can read the packet.

When the time to transfer the next CSP is reached during the asynchronous transfer, the transfer is not forcibly interrupted, and after the transfer is completed, the next CSP is transmitted. This gives 1
When one communication cycle continues for 125 μS or more, the next communication cycle period is shortened accordingly. By doing so, the 1394 network can maintain a substantially constant communication cycle.

(13) Device Map To create a device map, the application
As a means to know the topology of the 394 network, IE
According to the EE1394 standard, there are the following means.

1. Read the topology map register of the bus manager.

[0145] 2. It is estimated from the self ID packet at the time of bus reset.

However, according to the first and second means, although the topology of the cable connection order based on the parent-child relationship of each node is known, the topology of the physical positional relationship cannot be known. (There is also a problem that ports that are not mounted can be seen.) In addition, there is a method in which information for creating a device map is stored as a database other than the configuration ROM. The means to get depends on the protocol for database access.

By the way, the configuration ROM
The ability to read itself and the configuration ROM
A device that complies with the EEE1394 standard must have this. Therefore, by storing information such as device position and function in the configuration ROM of each node and giving them the function of reading them from the application,
The application of each node can implement a so-called device map display function without depending on a specific protocol such as database access and data transfer.

The configuration ROM can store physical positions, functions, and the like as node-specific information, and can be used to realize a device map display function.

In this case, as means for the application to know the 1394 network topology based on the physical positional relationship, at the time of bus reset or a request from the user,
By reading the configuration ROM of each node, it is possible to know the topology of the 1394 network. Furthermore, not only the physical position of the node but also various node information such as functions are described in the configuration ROM. By reading the configuration ROM, not only the physical position of the node but also the function information of each node can be obtained. Obtainable. The application is the configuration R of each node
When acquiring OM information, an API for acquiring arbitrary configuration ROM information of a designated node is used.

By using such means, the IE
The application of the device on the EE1394 network can create various device maps according to the use such as a physical topology map and a function map of each node, and the user can select a device having a necessary function. It is also possible.

The above is a general description of the configuration and functions of a data communication system configured using a 1394 serial bus.

[First Embodiment] Hereinafter, a first embodiment according to the present invention will be described.
An embodiment will be described.

<1394 Serial Bus Configuration> The configuration of the 1394 serial bus will be described below as a common part of each node connected to each local bus in this embodiment. FIG. 23 is a diagram showing a configuration of a 1394 serial bus block in a device (1394 node) connected by a 1394 serial bus in the present embodiment.

In FIG. 23, reference numeral 2701 denotes a link layer control IC (LINK-IC), which controls the interface with the device main body, and
02 (PHY-IC) data transfer, and of course implements the link layer function in the description of the 1394 serial bus described above. The main functions of the LINK-IC 2701 include a transmission / reception FIFO for temporarily storing transmission / reception data via the PHY-IC 2702, a packetization function of the transmission data, and a PHY-IC 2702 if the PHY-IC 2702 is a node address of reception data or synchronous transfer data. There is a function to determine whether the data is for the assigned channel, a receiver function to check the error of the data, and a function to interface with the device body (main block).

Reference numeral 2702 denotes a physical layer control IC (PHY-IC) for directly driving a 1394 serial bus.
And realizes the function of the physical layer in the 1394 serial bus described above. The main functions of the PHY-IC 2702 include bus initialization and arbitration, transmission data code encoding / decoding,
This includes monitoring the power supply state of the cable, supplying power for load termination (for recognition of active connection), and interface with the LINK-IC 2701.

2703 is a configuration ROM
, And the identification and communication conditions unique to each device are stored. The data format of the configuration ROM 2703 conforms to the format defined by the IEEE 1394 standard described above.

2704 is a LINK-IC 2701, P
A CPU 2805 for controlling the entire 1394 serial bus block including the HY-IC 2702 is a ROM in which a control program is stored.
The entire 94 serial bus block is controlled. 2706
Is a RAM, which is used as a data buffer for storing transmission / reception data, a control work area, and a data area of various registers mapped to 1394 addresses.

The 1394 nodes in the present embodiment each have a configuration RO as shown in FIG.
M, the software unit information of each device is in Unit directories, and the node-specific information is Node
It is stored in the dependent info directory.

The basic function instance of each device such as the printer function and the scanner function and detailed information accompanying the basic function can be held in an instance directory (Instance directory) offset from the Root Directory. .

Here, the configuration of the instance directory will be described. The instance directory stores information on devices such as printers and scanners that do not depend on the protocol. In the case of a single-function device, one piece of basic function information is stored. In the case of a device that supports a plurality of functions, a plurality of functions are listed and stored. Then, in addition to storing pointer information to a unit directory storing protocol / software information corresponding to each function, a pointer to a feature directory for storing specific detailed information related to each function is stored.

As shown in FIG. 6, in the address setting of the 1394 serial bus, the last 28 bits are secured as a data area unique to each model, which can be accessed from other devices connected to the 1394 serial bus. ing. FIG. 25 is a diagram showing an address space of a 28-bit area which is a model-specific data area.

In FIG. 25, from address 0000h to 02
A CSR core register section is arranged in the area of the address 00h. These registers exist as basic functions for node management defined in the CSR architecture.

The area from addresses 0200h to 0400h is defined by the CSR architecture as an area in which registers related to the 1394 serial bus are stored.

In the area from address 0800h to address 1000h, the current topology information of the 1394 serial bus and information on the transfer speed between nodes are stored. The area after the address 1000h is called a unit space, in which registers relating to operations unique to each device are arranged. In this area, a register section and a memory-mapped buffer area for data transfer defined by a higher-level protocol supported by each device, and a register unique to each device are arranged.

<Power Supply in System> In this embodiment, 139 having the above-described configuration shown in FIG.
A data communication system is constituted by devices having four serial bus blocks, and a cable connecting these devices is provided with a power supply line as shown in FIG.

FIG. 26 shows a circuit configuration around a power supply connector (hereinafter, referred to as a 1394 connector) in the 1394 node of this embodiment. Generally IEEE
A connector compliant with the E1394 standard (1394 connector) has six pins, one of which is arranged on a power supply line and the other is arranged on a ground line, as shown in FIG. 26, IC1 is a PHY-I shown in FIG.
This is a three-terminal regulator for supplying power to the C2702. The power supply to the IC1 is performed by a power supply line with one pin of the 1394 connector. When the power supply is provided in the main body of the device, the power supply from the main body is supplied through the diode D1 to the 1394 connector on the cathode side.
It is configured to cross the power supply line from pin 1 of the connector.

When the 1394 node (power supply node) of this embodiment supplies power to another node (power supply node), the power supply node supplies power by the self ID packet shown in FIG. The power amount which has been declared and permitted is output via the diode D1. Here, FIG. 27 shows a 3-bit field 1804 (Pw) indicating characteristics of power consumption and supply in the self ID packet.
The value of r) and its contents are shown.

On the other hand, in a power receiving node receiving power supply from another node, there is a power receiving node in which power is directly taken into a power supply IC in the main body from a power supply line of 1394 connector 1 pin, and a switch to a power supply line. In some cases, power is taken in when permission is given by arbitration in the Pwr field of the self ID packet.

The following environment is conceivable as the data communication system of the present embodiment in the form of power supply as described above.

FIG. 28 is a diagram showing a system in which a device (printer) provided with a main body driving adapter and a device (digital camera) using only a battery as a driving source are connected. The printer shown in the figure is a mobile printer that can be driven by a secondary battery and has an AC adapter for charging the battery and for driving the main body. The printer is connected to a digital camera driven only by a battery, which is a remarkable peer-to-peer environment (hereinafter referred to as a general home environment) in general homes.

As the power state of the printer in such a general home environment, the following several states can be considered.

1) Since the rechargeable battery is almost fully charged, there is no need to charge the rechargeable battery, and the driving power for the printer is supplied from the adapter.

2) The remaining capacity of the secondary battery is small, the adapter supplies power to the main body, and charges the secondary battery.

Here, a charging circuit (not shown) in the power receiving side device (digital camera in FIG. 28) of the present embodiment will be described.

FIG. 29 is a diagram showing a configuration of a charging circuit. In the figure, when the power supply for charging is supplied from an externally connected device, it is input via a diode D1.
When the self-power supply is used as the power source, the diode D2
Is entered via The charging circuit shown in FIG. 29 charges a nickel-metal hydride secondary battery, and supplies the input voltage by reducing the input voltage to a predetermined voltage by a step-down converter.

IC1 as a control IC has respective analog terminals for inputting a charging operation start permission signal (UV) and a charging current value as control signals thereof. Further, a switching signal is output from the SW terminal to the gate of the P-channel power MOSFET which is a main element of the step-down converter. Also, the charging current detecting resistor R1
The charging current is controlled by detecting the current from the potential difference between both ends of the charging current. Then, charging power is supplied to the nickel-metal hydride secondary battery with the voltage smoothed by the capacitor C1.

As the data communication system of this embodiment, in addition to the above-described example, a connection between devices receiving a stable power supply from an AC outlet, or a network in which three or more such devices coexist. Can be considered.

<Power Requirements in Nodes><< Connection of Three or More Nodes >> Hereinafter, for example, in an environment where three or more 1394 nodes are mixed and networked, a digital camera using a battery as a driving source is connected to a 1394 serial bus. A case will be described in which power supply is requested to another device connected by the above.

When the node ID is determined immediately after the bus reset, the digital camera sets the Pw of the self ID packet.
The r value is set to “111” and issued. As shown in FIG. 27, the Pwr value “111” indicates that “a node uses 1 W at the maximum when power is supplied from the bus, and 9 W is necessary to enable the link layer and the upper layer. Yes. " Before or after this, a self ID packet in which the Pwr value is set to “111” is also issued from another device that is expected to supply power, and the Pwr value is transmitted from the remaining one self-powered device. It is assumed that a self ID packet in which is set to “001” is issued.

In this case, depending on the result of the arbitration, the total amount of power demand exceeds the amount of supplied power, and therefore, at least one of the devices requesting power supply is supplied by the bus manager with power supply. Is rejected.

However, for example, the power requirement of a digital camera is in addition to the power requirement as its own power source for operation.
The power required is not necessarily required to be 9 watts because the battery is expected to charge the attached secondary battery pack. Therefore, in this embodiment, the digital camera issues a power request using its own self-ID packet, and issues a self-ID issued from another connected device after the bus reset.
Obtain the packet and confirm the consistency between the power supply and demand. Then, when the demand is large, the demand and the supply are matched by lowering the own demand level.

Hereinafter, power request control in the digital camera of the present embodiment will be described in detail.

Here, FIG. 30 shows the Pwr value of the self ID packet in the digital camera as the power receiving device,
Charge current value of secondary battery pack, and control IC of charge step-down converter for realizing the charge current value
The relationship between the PROG terminal of (IC1 in FIG. 29) and the set value of the D / A port in the CPU (A / Dset) is shown.

FIG. 31 is a flowchart showing power supply request control by the digital camera (power receiving side device) of the present embodiment.

When the digital camera is connected to the 1394 serial bus in a state where the capacity of its own secondary battery is slightly reduced, first, the digital camera uses its own operating power and power for charging the secondary battery. Expecting combined power supply, Pwr
As a value, “111” indicating a supply power of 9 [W] is selected, and a self ID packet is issued (S2701).

In this case, whether or not the power supply is possible is determined by the power arbitration by the bus manager. The digital camera itself also obtains a self ID packet issued from another connected device to obtain the power supply and demand. It confirms the consistency by itself (S2702). If it is determined by either the bus manager or the digital camera that the demand and supply of power are consistent, the maximum value of the charging current to the secondary battery of the digital camera is 980 from FIG. [MA], "52" is set as the A / D value for the charging current (S2703), and charging is started (S2714).

On the other hand, if the demand for electric power exceeds the supply, the digital camera issues a bus reset to lower the expected charging current by one level (S2704).
The wr value is changed to “110” and a self ID packet is issued (S2705).

Then, in the same manner as above, the consistency between the power demand and the supply is confirmed (S2706).
The digital camera sets "28" corresponding to the Pwr value "110" as the A / D value for the charging current (S270).
7), charging is started (S2714).

On the other hand, if the power demand still exceeds the supply, the digital camera issues a bus reset to further lower the expected charging current by one level (S270).
8) Change the Pwr value to "101" and issue a self ID packet (S2709).

Then, the consistency between the power demand and the supply is confirmed in the same manner as described above (S2710).
The digital camera sets “11” corresponding to the Pwr value “101” as the A / D value for the charging current (S271).
1), charging is started (S2714).

On the other hand, if the demand for power still exceeds the supply, the digital camera cannot operate with the power less than this, gives up the power reception, issues a bus reset (S2712), and sets the Pwr value to “100”. The self ID packet is issued after the change (S2709). That is, the digital camera requests only the minimum power necessary for its own operation, and does not charge the secondary battery.

In FIG. 31, power arbitration in which a request for the maximum supply amount of power is first made, and if not possible, the requested supply amount is sequentially reduced, has been described as an example. Arbitration is also conceivable in which a request for the supply amount is made, and thereafter, if there is sufficient power supply for the bus, the requested supply amount is gradually increased.

In the case of one-to-one connection as shown in FIG. 28, it is of course possible to directly issue a power supply request. The details will be described later.

After charging of the digital camera is started as described above, 139 is generated by the generated bus reset.
4 The network is initialized.

<< One-to-One Node Connection >> When only one device capable of supplying power through a 1394 serial bus is connected to a digital camera driven by a battery, the digital camera A case in which the device is requested to supply power will be described. This means that FIG.
In the general home environment shown in FIG. 7, the digital camera requests power supply to the printer.

The digital camera acquires the self ID packet of the printer immediately after the bus reset caused by the connection of a new device (in this case, a printer), so that only one printer is connected. If the printer is found to have power supply capability, the power supply is requested to the printer.

Here, FIG. 32 shows a Pwr value of a self ID packet issued from a printer as a power supply device,
Corresponding to the Pwr value, similarly to FIG. 30, the charging current value of the secondary battery pack in the digital camera receiving the power supply, and the A / D set value (A / D) for realizing the charging current value
set). For example, when the Pwr value of the self ID packet issued from the printer is “001”, 15 [W] is supplied, so that the charging voltage and the charging current in the digital camera are 8.2 [V] and 1.6, respectively.
[A], and the A / D set value for realizing it is “85”.

The digital camera uses its own operating power and 2
In order to obtain a power supply amount that satisfies the charging current value to the next assembled battery, the maximum value of the charging current is determined according to the table shown in FIG. 32, and power supply is requested.

FIG. 33 is a flowchart showing a power request control by a digital camera (see FIG. 28) as a power receiving device, which is connected one-to-one with a printer as a power supplying device.

When a printer is connected to the digital camera via a 1394 serial bus, the digital camera first acquires a self ID packet of the connected printer (S3001). Then, it is confirmed that only one device is connected (S3002), and further, it is confirmed that the device has power supply capability (S30).
03), confirm the Pwr value in the acquired self ID packet. Then, based on the table shown in FIG.
After setting the charging current A / D value according to the wr value (S3
005 to S3010), the printer declares acceptance of power by setting the Pwr value shown in FIG. 30 in its own self-ID packet, and starts charging (S3).
012, S3013).

On the other hand, if the Pwr value from the printer does not match any of those shown in FIG. 32, the digital camera does not make a charging request and receives power supply only to enable its own operation (S3011). .

If the number of devices connected to the digital camera is plural, or if the connected devices do not have power supply capability,
The power is supplied according to the ruling of the power management by the bus manager in the 94 network (S3004).

After the charging of the digital camera is started as described above, 139 is generated by the generated bus reset.
4 The network is initialized.

In the 1394 network of the present embodiment, when the supply voltage at the power supply side device is low, the maximum current of the communication cable conforming to the IEEE 1394 standard should not exceed 1.5 [A]. Take steps to confirm.

<Received Voltage Limit> In this embodiment, when one device receives power supply from the other device, the
On a communication cable conforming to the 1394 standard, a voltage is input in a range of 8 to 40 [V].

In this embodiment, the circuit configuration in the device is simplified by further restricting the voltage that can be used in the device within the above-mentioned voltage range.

FIG. 34 shows a configuration of a voltage limiting circuit for limiting the receiving voltage based on the input voltage in the power receiving device receiving the power supply. Hereinafter, the operation of the circuit will be described.
This will be described with reference to the flowchart shown in FIG.

In FIG. 34, the upper half including the PHY three-terminal regulator IC1 has the same configuration as that of FIG. 26, and a detailed description thereof will be omitted.

First, when the device does not have its own power supply (S 3601), when a voltage comes in from the power supply line by the connection by the communication cable, the voltage between the emitter and the base of the PNP transistor TR 1 is reduced. 0.6 [V] by the time constant of the resistor R3 and the capacitor C3
During this time, the power is supplied. When the TR1 is turned on, power is sent from the three-terminal regulator IC2 to the control IC IC3, and the IC3 starts control.

In IC3, first, Port1 is set to H
The level is output, and the transistor TR2 is turned on (S3602). Here, the IC 2 generates heat in accordance with the product of the current and the potential difference between the input voltage and the output voltage, and thus is not suitable for continuously receiving a high input voltage.

Thereafter, the IC 3 is connected to the A / D terminal Por
From t2, the input voltage is divided and input to the resistors R6 and R7 (S3603). Then, the input voltage is compared with a preset receivable voltage range (S3604), and if inappropriate, that is, out of the range, Port1 is set to a high impedance state (S3605), and transistor TR1 is turned off. And ends the control. Although not shown, the charge of the capacitor C3 can be discharged at the time of bus reset in the 1394 serial bus.

On the other hand, if the input voltage is within the receivable voltage range, after the bus reset (S3606), the self ID
Write the required power in the Pwr value of the packet and issue it (S
3607). If there is an instruction from the bus manager that power can be supplied (S3608), IC3 outputs Po.
After the L level is output from rt4, the power is supplied from the IC2 to other circuits in the device to perform initialization, and then the normal operation is started (S3609 to S3611).

If the power supply is refused as a result of the power arbitration by the bus manager after the self ID packet is issued (S3608), IC3 sets Port1 to the high impedance state (S3605), and transistor TR1 is turned off. And ends the control. Also, when the device has its own power supply (S3601),
Similarly, IC3 turns off Port1 (S360).
5).

As described above, according to the voltage limiting circuit shown in FIG. 34, only when the supply voltage is within the receivable voltage range, control is performed such that the voltage is received and another circuit is started. be able to.

FIG. 36 shows a configuration in which the voltage limiting circuit shown in FIG. 34 further includes a step-down converter circuit for driving an actuator (motor). Hereinafter, the operation of the circuit will be described with reference to the flowchart shown in FIG.

The step-down converter shown in FIG. 36 includes a transistor TR4, a Schottky diode D3,
The choke coil L1 operates by being controlled by the IC4.

In order for the step-down converter circuit to operate normally in the configuration shown in FIG. 36, an input higher than the set voltage is required. Therefore, in the operation of the voltage limiting circuit shown in FIG. 36, similarly to the case of the circuit shown in FIG. 34, after the IC 3 detects the input voltage at the Port 2 (S3801 to S3803), the voltage determination is performed in the manner described below. Do.

It is determined whether or not the input voltage is higher than the set receivable voltage (S3804).
ort1 is set to a high impedance state (S380).
5) The control is terminated after the transistor TR1 is turned off.

On the other hand, if the input voltage is higher than the set voltage, after the bus reset (S3806), the required power is entered in the Pwr value of the self ID packet and issued (S38).
07). If there is an instruction from the bus manager to enable power supply (S3808), IC3 issues an enable signal to IC4 (S38).
09), Port 4 output from IC 4 is permitted, power is supplied to the motor, and operation of the motor is permitted (S3).
810-S3811).

<Power supply control accompanying change in power supply capacity> In an apparatus equipped with a secondary battery and an adapter for driving the main body and charging the secondary battery, such as the printer shown in FIG.
The power supply control when the charging current changes during the charging operation of the next battery will be described.

FIG. 38 is a diagram showing a configuration of a connector portion for taking in power from the adapter to the main device in the above device, and the power consumption in the main body is detected by the configuration.

In the same figure, the connector of the adapter has a two-pin configuration, one pin is connected to a power supply line (VDD), and the second pin is connected to the ground.

Further, a smoothing capacitor C1 is inserted in the power supply line from pin 1, and a minute value resistor R1
Are inserted in series. By detecting the potential difference between both ends of the minute value resistor R1 by the amplifier Amp1, the power supply current (VDD current) during charging can be detected as a voltage value at the A / D terminal of the control IC inside the device. Note that the VDD current is determined by the power consumption of the device main body and 2
This is detected as the sum of the power for charging the next battery.

FIG. 39 shows Pw in the self ID packet of the device based on the VDD current state detected during charging.
It is a flowchart which shows the process which sets an r value.

When the detected VDD current value is 1.6 [A] or more, the device does not supply power to the serial bus. That is, "000" is set as the Pwr value (S410).
3).

When the VDD current is less than 1.6 [A],
When it is 0.8 [A] or more, the power supply of 15 [W] is permitted. That is, “001” is set as the Pwr value (S
4104).

When the VDD current is less than 0.8 [A], power supply of 30 [W] is permitted. That is, “010” is set as the Pwr value (S4105).

The 1394 network is initialized by the bus reset that occurs after the setting of the Pwr value.

As described above, when the value of the detected VDD current changes, the Pwr value in the self ID packet is rewritten and a bus reset is issued, so that the power supply during charging is performed according to the change in the supply capacity. Adaptive control.

When the device detects that power supply is requested by Pwr of a self ID packet from a connection partner (for example, a digital camera) in a peer-to-peer environment as shown in FIG. The charging current to the middle secondary battery is limited, and at the time when the power supply to the partner device becomes possible, its own Pwr value is set and a bus reset is issued. That is, priority is given to supplying power to the partner device over charging the own secondary battery.

FIG. 40 shows the relationship between the power supply request from the connection partner and the charging current to the own secondary battery.
The charging voltage in this case is 15 [V]. According to the figure, it can be seen that as the required power from the partner device increases, its own charging current decreases.

As described above, according to the present embodiment,
Maximizing the supply capacity on the power supply side by reducing the required power amount by limiting the functions on the power requesting apparatus based on the balance between the power demand and supply between the apparatuses connected by the 1394 serial bus It is possible to provide more effective power supply by utilizing.

[Second Embodiment] Hereinafter, a second embodiment according to the present invention will be described.
An embodiment will be described.

In the first embodiment described above, FIG.
As described above, the power supply control in the system in which the device having the adapter for driving the main body and the device using only the battery as the driving source are connected by the 1394 serial bus has been described. In the second embodiment, a description will be given of power supply control in a system in which devices using only batteries as driving sources are connected to each other via a 1394 serial bus.

FIG. 41 is a diagram showing a peer-to-peer system in which devices using only batteries (primary or secondary) as driving sources are connected. As a usage form of the system, for example, outdoor communication under a so-called mobile environment in which mobile terminals are connected to each other is assumed. FIG. 41 shows an example in which a mobile printer as an output device and a digital camera as an input device are connected.

In general, a device whose driving power source is only a battery can hardly supply power to a connected partner device. Therefore, in the self ID packet after the bus reset, the Pwr value does not indicate power supply.

However, in such a system in which battery-operated devices are connected to each other, the operation of the system becomes impossible when the remaining capacity of the battery in any of the devices is reduced to a predetermined amount. .

In the second embodiment, in order to solve such a problem, when the remaining battery power of one device decreases, the power supply is requested to the other device, thereby operating the system. Continue to the maximum.

FIG. 42 is a flowchart showing power control in a device (power receiving side device) which requests power supply in a system in which battery-driven devices are connected to each other.

First, the above-described configuration R
If the power value required by the device is not registered in the instance directory in the OM, information indicating that the device is currently operating on a battery is written (S310).
1, S3102).

When the remaining battery power falls below a predetermined value, "RQ Bat" is registered as a keyword indicating the power request in the instance directory in order to make a power request to the partner device. The following items are registered (S3103, S3104).

The operation is performed only with the battery. The required power (MODE1). The required power (MODE2). The receivable voltage range. MODE1 indicates the mode in which the overall operation of the device body is performed. Indicates a mode in which comprehensive operation of the device main body is not possible, but only limited operation is possible. Therefore, the amount of power supplied in MODE2 is MO
It is less than in the case of DE1.

After completing the above registration in the instance directory, the device issues a bus reset (S31).
05), it waits for the generation of a keyword “RESP Bat” indicating a response to the power request in the instance directory in the configuration ROM of the partner device (S3106).

If there is no answer from the partner device even after waiting for a predetermined time, or if an answer of “NG” is read (S3107), “WeekB” indicating that the remaining battery capacity is insufficient is displayed.
By issuing the “attery”, the power of the device is turned off (S3111, S3112).

On the other hand, if the response from the partner device indicates that power supply is permitted, the power supply time from the partner device is limited (details will be described later), and the permitted supply power amounts are set to MODE1 and MODE2. (For example, whether or not the required power in MODE1 is satisfied), and the power is supplied by setting the operation in the configuration ROM (S3107 to S3).
110).

The power control on the power receiving side device has been described above. Next, the power control on the power supplying side device will be described.

FIG. 43 is a flowchart showing power control in a device (power supply device) for supplying power in a system in which battery-driven devices are connected to each other.

First, the configuration ROM of the partner device is read (S3201). If only one keyword “RQBat” indicating a power request is registered in the instance directory, the required power amount is read (S3201). At this time,
Reads the self ID packet of the partner device, and writes its Pwr
It is also confirmed based on the value that power is not currently being supplied.

Then, the device reads the remaining capacity of the battery, which is its own driving source, and refers to the table showing the relationship between the suppliable power and the remaining capacity shown in FIG. It is determined whether any of the powers corresponding to MODE2 can be supplied (S320).
3, S3204).

Here, with reference to FIGS. 44 and 45, a method of determining whether the required power can be supplied will be described in detail.

FIG. 44 is a diagram showing the relationship between the remaining battery charge and the suppliable power. In the figure, Table 1 is a table showing the amount of power that can be supplied to the partner device while the device body is performing a normal operation, and Table 2 is the amount of power that can be supplied to the partner device side by restricting the operation of the device body. FIG.

FIG. 45 is a flowchart showing a power supply availability determination process using the table. First, MO
It is assumed that the determination process for the required power amount of DE1 is performed.

The read required power amount of the partner device is defined as Ta
ble1 (S3401), and when it is determined that the required power amount is larger, that is, the required power amount does not satisfy Table1,
Next, the required power amount is compared with the remaining battery capacity obtained by Table 2 (S3402). As a result, the required power amount is still larger, that is, the required power amount is Tabl.
If it is determined that e2 is not satisfied, it is determined that the supply of the required power is impossible (S3403).

Of course, step S3401 or S34
02, the required power is smaller than the remaining battery capacity, that is, the required power is less than Table1 or Ta.
If it is determined that any of ble2 is satisfied,
It is determined that the supply of the required power is possible (S34).
04).

The above determination process is first performed for the required power amount of MODE1, and if it is determined that supply is impossible,
Next, a similar determination is made for the required power amount of MODE2.

Returning to FIG. 43, if it is determined in step S3204 that supply is possible, one of the time tables (Ta) shown in FIG.
ble1 or Table2) (S320)
5).

FIG. 46 is a diagram showing the relationship between the suppliable power and the time (permission time) during which continuous supply is possible. In the same drawing, Table 1 is a table showing the time during which the device main body can supply the other device while performing normal operation, and Table 2 shows the time during which the operation of the device main body can be supplied to the other device side by restricting the operation of the device body. It is a table. Which one of these is selected is determined based on which of the tables shown in FIG.

Thereafter, its own configuration R
In the instance directory in the OM, "RESP" which is a keyword indicating a response to a power request is stored.
Bat "is registered, and the following items are registered as its contents (S3206).

The type of MODE to be permitted (MODE1 / MODE1 /
MODE2)-Time during which power can be continuously supplied-Type of own operation table (Table1 / Table)
e2) ・ Supply voltage range Then, a bus reset is issued (S320)
8) Release the power supply on the communication cable with the partner device.

After the supply or reception of power is started as described above, when the set continuous supply time elapses, the power supply side device issues a bus reset and ends the power supply. Note that the power supply-side device performs an operation corresponding to either the selected Table 1 or Table 2 during power supply. That is, when Table 1 is selected, the normal operation is performed, and when Table 2 is selected, a limited operation with lower power consumption than that of Table 1 is performed.

As described above, according to the second embodiment, in a system in which devices that use only a battery as a drive source are connected, even if the remaining capacity of the battery in one device decreases to a predetermined amount, Since it is possible to request the power supply after limiting the function of the device in accordance with its power supply capability, the operation as a system can be continued to the maximum extent.

In the system of the second embodiment, the Pwr of the self ID packet after the bus reset is
Even if the value does not require power supply, by registering the corresponding voltage range as the keyword "RQBat" in the instance directory in the configuration ROM, the same receiving voltage limitation as in the first embodiment described above is performed. That is, it is possible to restrict the operation of the device to only the adaptive voltage range.

[0263]

[Other Embodiments] Even if the present invention is applied to a system including a plurality of devices (for example, a host computer, an interface device, a reader, a printer, etc.), an apparatus (for example, a copying machine) Machine, facsimile machine, etc.).

An object of the present invention is to supply a storage medium (or a recording medium) in which a program code of software for realizing the functions of the above-described embodiments is recorded to a system or an apparatus, and to provide a computer (or a computer) of the system or the apparatus. Or a CPU or MPU) reads out and executes the program code stored in the storage medium,
It goes without saying that this is achieved. In this case, the program code itself read from the storage medium implements the functions of the above-described embodiment, and the storage medium storing the program code constitutes the present invention.
In addition, by executing the program code read by the computer, not only the functions of the above-described embodiments are realized, but also based on the instructions of the program code,
The operating system (OS) running on the computer performs part or all of the actual processing,
It goes without saying that a case where the function of the above-described embodiment is realized by the processing is also included.

Further, after the program code read from the storage medium is written in the memory provided in the function expansion card inserted into the computer or the function expansion unit connected to the computer, the program code is read based on the instruction of the program code. , The CPU provided in the function expansion card or the function expansion unit performs part or all of the actual processing,
It goes without saying that a case where the function of the above-described embodiment is realized by the processing is also included.

[0266]

As described above, according to the present invention,
It is possible to optimize the power supply balance between devices connected by a serial bus based on the IEEE 1394 standard.

[Brief description of the drawings]

FIG. 1 is a diagram showing a general configuration example of a system to which the present invention is applied.

FIG. 2 is a diagram showing a network configuration using a 1394 serial bus.

FIG. 3 is a diagram illustrating a configuration example of a 1394 serial bus.

FIG. 4 is a diagram showing services in a link layer of a 1394 serial bus.

FIG. 5 is a diagram showing services in a transaction layer of a 1394 serial bus.

FIG. 6 is a diagram showing an address space of a 1394 serial bus.

FIG. 7 is a diagram showing the function of the CSR architecture of the 1394 serial bus.

FIG. 8 is a diagram showing registers related to a 1394 serial bus.

FIG. 9 is a diagram showing a minimum format of a configuration ROM of a 1394 serial bus.

FIG. 10 is a diagram showing a general format of a configuration ROM of a 1394 serial bus.

FIG. 11 is a diagram showing registers relating to node resources of the 1394 serial bus.

FIG. 12 is a diagram showing a cross section of a cable for a 1394 serial bus.

FIG. 13 is a diagram illustrating a DS-Link system.

FIG. 14 is a diagram illustrating a network operation example of a 1394 serial bus.

FIG. 15 is a flowchart showing a sequence from a bus reset to a node ID setting.

FIG. 16 is a flowchart illustrating details of a parent-child relationship declaration process.

FIG. 17 is a flowchart illustrating details of a node ID setting process.

FIG. 18 is a diagram illustrating a configuration example of a self ID packet.

FIG. 19 is a diagram illustrating arbitration.

FIG. 20 is a diagram showing a temporal transition of a transfer state when a synchronous transfer mode and an asynchronous transfer mode are mixed.

FIG. 21 is a diagram illustrating an example of a packet format for synchronous transfer.

FIG. 22 is a diagram illustrating an example of a packet format for asynchronous transfer.

FIG. 23 is a diagram illustrating a configuration of a 1394 serial bus block in a node according to the present embodiment.

FIG. 24 is a diagram showing a configuration of a configuration ROM in a node according to the present embodiment.

FIG. 25 is a diagram illustrating an address space of a unique data area in a node according to the present embodiment.

FIG. 26 is a diagram illustrating a circuit configuration around a power supply connector in a 1394 node according to the present embodiment.

FIG. 27 is a diagram showing a list of Pwr values in the present embodiment.

FIG. 28 is a diagram illustrating a one-to-one connection configuration between a battery-driven device and an AC-driven device according to the present embodiment.

FIG. 29 is a diagram showing a configuration of a charging circuit in a power receiving side device of the present embodiment.

FIG. 30 is a diagram showing a power request table and a charging current table in the power receiving side device of the present embodiment.

FIG. 31 is a flowchart showing power request control in the power receiving side device of the present embodiment.

FIG. 32 is a diagram showing a power supply table and a charging current table in the power supply side device of the present embodiment.

FIG. 33 is a flowchart showing power request control in the power receiving device of the present embodiment.

FIG. 34 is a diagram showing a configuration of a voltage limiting circuit that limits a received voltage in the power receiving device of the present embodiment.

FIG. 35 is a flowchart showing an operation in the voltage limiting circuit of FIG. 34;

FIG. 36 is a diagram showing a configuration of a voltage limiting circuit that limits a received voltage to a high voltage in the power receiving device of the present embodiment.

FIG. 37 is a flowchart showing an operation in the voltage limiting circuit of FIG. 36;

FIG. 38 is a diagram showing a peripheral configuration of a power connector according to the present embodiment.

FIG. 39 shows Pwr based on a current state in the present embodiment.
It is a flowchart which shows a value setting process.

FIG. 40 is a diagram showing a relationship between a power supply request from a connection partner and a charging current to the secondary battery of the present embodiment.

FIG. 41 is a diagram illustrating a connection configuration between battery-powered devices according to the second embodiment.

FIG. 42 is a flowchart showing power request control by battery driving in the second embodiment.

FIG. 43 is a flowchart illustrating power supply control in response to a power request from a battery-driven device according to the second embodiment.

FIG. 44 is a diagram showing a relationship between remaining battery capacity and suppliable power in the second embodiment.

FIG. 45 is a flowchart illustrating a power supply availability determination process according to the second embodiment.

FIG. 46 is a diagram illustrating a relationship between suppliable power and a permitted time in the second embodiment.

Claims (29)

[Claims] 1. A data communication system in which a power supply device and a power receiving device are connected by a serial bus capable of supplying power, wherein the power receiving device issues request information indicating a required amount of power. Acquiring means for acquiring supply information indicating the suppliable power amount in the power supply device; and when the required power amount indicated by the request information is appropriate for the suppliable power amount indicated by the supply information, Power receiving means for receiving power based on the required power amount from the power supply device, and operating means for selectively executing a plurality of operation modes according to the power amount received by the power receiving means. The issuance means, if the requested power amount indicated by the issued request information is not appropriate for the suppliable power amount indicated by the supply information, In this case, the required power amount is changed so that any one of the operation modes of the operation means can be executed, and the request information is reissued. 2. The data communication system according to claim 1, wherein the issuing unit re-issues the request information by gradually reducing the required power amount. 3. The method according to claim 1, wherein the serial bus is an IEEE1394.
2. The data communication system according to claim 1, wherein the bus conforms to or conforms to a standard. 4. The issuing unit issues the request information and the acquiring unit acquires the supply information.
4. The data communication system according to claim 3, wherein the data communication is performed after a bus reset in the serial bus. 5. The data communication system according to claim 2, wherein said issuing means issues said request information by a self ID packet of said power receiving device. 6. The data communication system according to claim 2, wherein said acquisition means acquires said supply information by a self ID packet issued from said power supply device. 7. The data according to claim 1, wherein the operation means has a plurality of operation modes for charging a battery serving as a drive source of the power receiving device in accordance with a plurality of levels of electric energy. Communications system. 8. An operation mode in which the battery is not charged when the amount of power received by the power receiving unit is less than a predetermined minimum amount of power. 8. The data communication system according to 7. 9. The power receiving means, when the supply of the required power amount indicated by the request information is permitted based on power arbitration by a bus manager of the serial bus, the power receiving unit converts the power based on the required power amount into the power amount. The data communication system according to claim 1, wherein the data is received from a power supply device. 10. The data communication system according to claim 1, wherein said power receiving device further includes voltage limiting means for limiting a voltage received by said power receiving means to be within a predetermined range. 11. The power supply device has means for charging its own secondary battery, and the charging current to the secondary battery decreases as the amount of power required from the power receiving device increases. The data communication system according to claim 1, wherein 12. The data communication system according to claim 1, wherein the power supply device includes an AC power adapter. 13. A data communication system in which a first device and a second device using a battery as a driving source are connected to each other by a serial bus capable of supplying power, wherein the first device has a remaining battery capacity. Issuing means for issuing, to the second device, request information indicating a required power amount in a plurality of stages when the power amount becomes equal to or less than a predetermined amount; and a response to power supply from the second device based on the request information And a power receiving means for receiving, from the second device, power based on the required amount of power at the permitted stage when power supply is permitted by the answer, and The data communication system according to claim 1, wherein the required power amount at each stage is a required power amount corresponding to each of a plurality of operation modes in the first device. 14. The serial bus is an IEEE 139
14. The data communication system according to claim 13, wherein the bus conforms to or conforms to four standards. 15. The data communication system according to claim 14, wherein said issuing means issues said request information by using a configuration ROM in said first device. 16. The data communication system according to claim 14, wherein said obtaining means obtains said answer by using a configuration ROM in said second device. 17. The power supply for turning off the power of the first device when the power supply from the second device is rejected by the response obtained by the obtaining unit. 14. The data communication system according to claim 13, further comprising an off unit. 18. The second device, holding means for holding a table indicating a relationship between its own remaining battery capacity and suppliable power in accordance with its own plurality of operation modes, respectively, Judging means for judging which table can supply power based on the request information by referring to the table based on the request information from the device; and Answering means for answering whether power supply to the request information from the first device is possible, and performing the operation in an operation mode based on a table determined to allow power supply by the determining means, 14. The data communication system according to claim 13, further comprising power supply means for supplying power to one device. 19. The apparatus according to claim 1, wherein the second device further replies a continuous supply possible time of the power when the power supply to the first device is possible.
9. The data communication system according to 8. 20. In a data communication system in which a power supply device and a power supply device are connected by a serial bus capable of supplying power, the power supply device issues request information indicating a required power amount, and the power supply device Issues supply information indicating the suppliable power amount, and when the required power amount indicated by the request information is appropriate for the suppliable power amount indicated by the supply information, the power based on the required power amount is The power supply device supplies the power to the power receiving device.The power receiving device executes one of a plurality of stages of operation modes according to the amount of power supplied in the power supply process. If the requested power amount indicated is not appropriate for the suppliable power amount indicated by the supply information, the requested power amount is The power control method of a data communication system, characterized in that to reissue the changes to request information as one of the operation modes be executed in the operation unit. 21. In a data communication system in which a first device and a second device driven by a battery are connected to each other by a serial bus capable of supplying power, the first device has a remaining battery capacity. Issuing request information indicating a required power amount in a plurality of stages to the second device when the amount becomes equal to or less than the fixed amount, the second device issues permission / prohibition of power supply based on the request information, The second device, when permitting power supply according to the answer, supplies power to the first device based on the required power amount at the permitted stage, and the required power amount at the plurality of stages is the first power amount. A power control method for a data communication system, wherein the required power amount corresponds to a plurality of operation modes in a device. 22. The serial bus is an IEEE 139
22. The power control method for a data communication system according to claim 20, wherein the bus conforms to or conforms to four standards. 23. A recording medium recording a program for implementing the control method for a data communication system according to claim 20. 24. A power receiving device connected to a power supply device by a serial bus capable of supplying power, an issuing unit for issuing request information indicating a required amount of power, and an suppliable power in the power supply device. Obtaining means for obtaining supply information indicating the amount, and when the required power amount indicated by the request information is appropriate for the suppliable power amount indicated by the supply information, the power based on the required power amount Power receiving means for receiving from the power supply device, and operating means for selectively enabling a plurality of operation modes in accordance with the amount of power received by the power receiving means; When the required power amount indicated by the request information is not appropriate for the suppliable power amount indicated by the supply information, the required power amount is changed by any of the operation means. Power receiving apparatus characterized by reissuing the request information to change so that the operation mode can be executed in. 25. The power receiving apparatus according to claim 24, wherein the issuing unit re-issues the request information by gradually reducing the required power amount. 26. A power receiving apparatus powered by a battery, connected to a device powered by a battery via a serial bus capable of supplying power, wherein the remaining battery capacity falls below a predetermined amount. Issuing means for issuing, to the device, request information indicating a required power amount in a plurality of stages; acquiring means for acquiring a response to power supply from the device based on the request information; and Power receiving means for receiving, from the device, power based on the required amount of power at the permitted stage when the device is permitted, and the required amount of power at the plurality of stages corresponds to a plurality of operation modes in the apparatus. A power receiving device characterized by a corresponding required amount of power. 27. The serial bus is an IEEE 139
27. The power receiving apparatus according to claim 25, wherein the bus conforms to or conforms to four standards. 28. A data communication system in which a power supply device and a power reception device are connected by a serial bus capable of supplying power, wherein the power reception device issues request information indicating a required amount of power. An acquisition unit that acquires supply information indicating an amount of power that can be supplied by the power supply device; a power reception unit that receives power from the power supply device; and a plurality of operation modes in which power amounts required for operation are different Operating means, the issuing means, when the required power amount indicated by the issued request information is not appropriate for the suppliable power amount indicated by the supply information, the issuing power unit A data communication system, wherein any one of the operation modes in the operation means is changed to be executable. 29. In a data communication system in which a power supply device and a power supply device are connected by a serial bus capable of supplying power, the power supply device issues request information indicating a required power amount, and the power supply device Issues supply information indicating the amount of power that can be supplied, supplies power to the power receiving device from the power supply device, the power receiving device has a plurality of operation modes in which the amount of power required for operation is different, If the requested power amount indicated by the issued request information is not appropriate for the suppliable power amount indicated by the supply information, the requested power amount is determined to be executable in any one of the operation modes in the operation means. A power control method for a data communication system, comprising: