JP2009199106A - Interface circuit, electronic device having interface circuit, communication system and voltage switching method - Google Patents

Abstract

In a communication system capable of selecting an operation voltage from a plurality of interface voltages, the interface voltage switching process is stably performed during operation of the communication system.
In response to a command to lower the interface voltage from the host device, the slave device switches the interface voltage, and then the slave device determines that the interface circuit operates stably. Notify completion of voltage switching of interface circuit. At that time, the notification from the slave device to the host device always maintains the signal level based on the voltage on the host device side on the signal line used for the existing interface. In addition, the host device performs voltage switching of the host side interface after the interface voltage switching of the slave device is completed.
[Selection] Figure 4

Description

  The present invention provides an interface circuit capable of stably and efficiently switching an interface voltage during operation of a host device and a slave device in a communication system capable of selecting an operation voltage from a plurality of interface voltages, and the interface circuit The present invention relates to an electronic device including the above, a communication system, and a voltage switching method.

  In recent years, slave devices such as card-shaped SD cards and memory sticks, which have high-capacity nonvolatile memory elements such as flash memory and can process data at high speed, have become popular in the market. Personal computers and PDAs (Personal Digital Assistants) It is used in host devices that can use slave devices such as mobile phones, digital cameras, audio players, and car navigation systems.

  Recently, in addition to the memory function, for example, a wireless LAN function, a network connection function such as wireless communication based on the Bluetooth (registered trademark) standard, a position measurement function using GPS (Global Positioning System), terrestrial digital television broadcasting Slave devices equipped with input / output functions such as the one-segment broadcasting reception function have also appeared, and host devices can connect these slave devices and use the functions installed in the slave devices.

 In such a communication system using a host device and a slave device, the amount of data to be processed increases year by year, and there is a strong demand from the market for improving the interface speed between the host device and the slave device. On the other hand, it is also a very strong demand from the market to maintain interface compatibility so that existing interfaces that are popular in the market can be used continuously.

  It is effective to reduce the interface voltage in order to improve the interface processing speed by utilizing the existing interface circuit.

In conventional host devices and slave devices that can select an operating voltage from a plurality of interface voltages, a discrimination key that indicates the type of interface voltage between the host device and the slave device is provided, and the host device is an interface for the slave device. A technique is used in which the interface voltage is determined by switching the voltage supplied to the slave device after detecting the voltage (see, for example, Patent Document 1).
JP 2002-169631 A

However, in the above-described conventional technology, a dedicated terminal for determining the interface voltage is required for each interface voltage, and there is a problem that it is difficult to apply to the existing interface standard in which the number of interfaces has already been determined. ,
In addition, because the host device determines the interface voltage by detecting the discrimination key from the slave device, when switching the interface voltage during operation, it is determined whether the switching of the interface voltage of the slave device has been completed normally. There is a problem that it is difficult to ensure the reliability of the communication system.

  Furthermore, in the conventional technology, the interface voltage between the host device and the slave device is premised on the same level as the voltage supplied from the host device to the slave device, and the interface voltage can be changed without changing the operating voltage of the slave device. There has been a problem that it is difficult to stably switch the voltage of only the circuit during operation.

  The object of the present invention is to solve the above-mentioned problems, and to perform switching control of only the interface voltage between the host device and the slave device with the same number as the existing interface standard and more reliably than the conventional technology. An interface circuit, an electronic device including the interface circuit, a communication system, and a voltage switching method are provided.

The interface circuit according to the first invention is:
A communication system in which at least one of the at least two electronic devices serves as a host device between at least two electronic devices, and performs master-slave communication with at least one slave device of the at least two electronic devices. An interface circuit provided in the slave device,
The interface circuit is
Means for continuously outputting the H level at the voltage level before switching to the host device during the interface voltage switching of the slave device when lowering the interface voltage between the host device and the slave device;
Means for outputting an L level after completion of switching of the interface voltage of the slave device.

  In order to maintain the voltage level before switching, means for using a pull-up resistor connected to the host-side power supply is provided.

A means for disconnecting the pull-up resistor after completion of the voltage switching is provided.
A communication device according to the second invention is:
The interface circuit according to the first invention is provided.
An interface circuit according to a third invention is
An interface circuit provided in the host device in a communication system that performs communication by connecting at least two electronic devices (host device and slave device),
The interface circuit is
Means for detecting completion of interface voltage switching of the slave device when lowering the interface voltage between the host device and the slave device;
Means for switching the interface voltage of the host device after completion of the interface voltage switching of the slave device;
It is provided with.
A communication device according to a fourth invention is
An interface circuit according to the third invention is provided.
A communication device according to a fifth invention is
An electronic device according to the second invention and an electronic device according to the fourth invention are provided.
The voltage switching method according to the sixth invention is:
A communication system in which at least one of the at least two electronic devices serves as a host device between at least two electronic devices, and performs master-slave communication with at least one slave device of the at least two electronic devices. In reducing the interface voltage between the host device and the slave device in
During the interface voltage switching of the slave device, the slave device continues to output H level at the voltage level before switching from the slave device to the host device;
Outputting L level from the slave device to the host device after completion of interface voltage switching of the slave device;
Detecting an L level from the slave device and switching an interface voltage of the host device.
An interface circuit according to a seventh invention is
A communication system in which at least one of the at least two electronic devices serves as a host device between at least two electronic devices, and performs master-slave communication with at least one slave device of the at least two electronic devices. An interface circuit provided in the host device,
The interface circuit is
Means for continuously outputting an H level at a level equal to or higher than the voltage before switching to the slave device during the interface voltage switching of the host device when raising the interface voltage between the host device and the slave device;
Means for outputting L level after completion of interface voltage switching of the host device;
It is provided with.
An electronic device according to an eighth invention is
An interface circuit according to the seventh invention is provided.
An interface circuit according to a ninth invention is
A communication system in which at least one of the at least two electronic devices serves as a host device between at least two electronic devices, and performs master-slave communication with at least one slave device of the at least two electronic devices. In the interface circuit provided in the slave device,
The interface circuit is
Means for outputting an L level during switching of the interface voltage of the host device when raising the interface voltage between the host device and the slave device;
Means for detecting completion of interface voltage switching of the host device and means for switching interface voltage of the slave device after completion of interface voltage switching of the host device;
Means for outputting an H level at the voltage level after switching after completion of the interface voltage switching of the slave device;
It is provided with.
An electronic device according to a tenth invention is
An interface according to the ninth invention is provided.
A communication system according to the eleventh invention is
An electronic device according to an eighth invention and an electronic device according to the tenth invention are provided.
The voltage switching method according to the twelfth invention is
A communication system in which at least one of the at least two electronic devices serves as a host device between at least two electronic devices, and performs master-slave communication with at least one slave device of the at least two electronic devices. In raising the interface voltage between the host device and the slave device in
Outputting an L level from the slave device during switching of the interface voltage of the host device;
Continuing to output H level from the host device to the slave device at a level equal to or higher than the voltage before switching;
Outputting L level to the slave device after completion of interface voltage switching of the host device;
Detecting L level from the host device and switching the interface voltage of the slave device;
And outputting the H level at the voltage level after switching after the interface voltage of the slave device has been switched.

  According to the interface circuit, the electronic device including the interface circuit, the communication system, and the voltage switching method according to the present invention, the slave device switches the interface voltage of the slave device in response to the interface voltage change command from the host device. After that, when notifying completion of voltage switching to the host device, communication at a signal level based on the voltage on the host device side is always possible on at least two signal lines used for existing interfaces. Therefore, the switching control of the interface voltage can be executed with the same number as that of the existing interface standard and without waste of time as compared with the prior art.

Hereinafter, embodiments according to the present invention will be described with reference to the drawings. In addition, in each following embodiment, the same code | symbol is attached | subjected about the same component.
(First embodiment)
FIG. 1 is a diagram showing a configuration of a communication system according to the first embodiment of the present invention.
In FIG. 1, 1 is an electronic device such as a digital camera or a mobile phone, and 2 is an electronic device having an input / output device such as a memory card or an I / O card. Further, the electronic device 1 and the electronic device 2 constitute a communication system, and the electronic device 2 operates with power supplied from the electronic device 1 via the power line 40, and the clock signal 52 and the two signal buses 50 and 51 are operated. The master / slave communication is performed using the electronic device 1 as a master device and the electronic device 2 as a slave device.

  In FIG. 1, the electronic device 1 includes a voltage source 10 having a first voltage (for example, 3.3 V) and a regulator 11 that operates from the first voltage supplied from the voltage source 10. Here, the regulator 11 can output a first voltage supplied from the voltage source 10 or a second voltage (for example, 1.8 V) newly generated from the first voltage.

The electronic device 1 is further driven by an interface voltage supplied from the regulator 11, and a first input / output buffer 16 that exchanges data with the electronic device 2 via the signal bus 50,
Similarly, a second input / output buffer 17 that is driven by an interface voltage supplied from the regulator 11 and that exchanges data with the electronic device 2 via the signal bus 51;
Similarly, a first output buffer 18 that is driven by an interface voltage supplied from the regulator 11 and transmits a clock to the electronic device 2 via the signal bus 52;
A pull-up resistor 19 for pulling up the bus 51 to a voltage level supplied from the regulator 11;
Means for issuing a command for switching the interface voltage between the electronic device 1 and the electronic device 2, and means for controlling a voltage supplied from the regulator 11 in accordance with a signal from the input / output buffer 16 or the input / output buffer 17. A controller 13 having
A detection circuit 12 for detecting the output voltage of the regulator 11;
When the controller 13 performs control to switch the output voltage of the regulator 11, the interface voltage of the electronic device 1 is normally switched to the voltage range designated by the controller 13 based on the output of the detection circuit 12, and the buffers 16 to 18 are stabilized. A stabilization waiting circuit 15 for determining whether or not the state has shifted to an operable state,
When the controller 13 issues an interface voltage switching command, means for notifying the electronic device 2 from the input / output buffer 17 via the bus 51 that the interface voltage switching operation of the electronic device 1 is in progress, and a stabilization wait circuit 15 A means for transmitting from the input / output buffer 17 via the bus 51 to the electronic device 2 that the transition of the interface voltage of the electronic device 1 has been completed normally after determining that the interface voltage of the electronic device 1 has been switched normally. An output control circuit 14 for controlling the supply of a clock from the output buffer 18 to the electronic device 2 via the bus 52;
Consists of

  In FIG. 1, the electronic device 2 includes a regulator 21 that operates from a first voltage supplied via the power line 40. Here, the regulator 21 can output a first voltage supplied from the power line 40 or a second voltage newly generated from the first voltage. Here, the second voltage is a voltage level equivalent to the second voltage level generated by the regulator 11 of the electronic device 1.

Furthermore, the electronic device 2 is driven by the interface voltage supplied from the regulator 21, and a first input / output buffer 26 that performs data exchange with the electronic device 1 via the signal bus 50,
Similarly, a second input / output buffer 27 that is driven by an interface voltage supplied from the regulator 21 and that exchanges data with the electronic device 1 via the signal bus 51;
Similarly, a first input buffer 28 that is driven by an interface voltage supplied from the regulator 21 and that exchanges data with the electronic device 1 via the signal bus 52;
A detection circuit 22 for detecting the output voltage of the regulator 21;
A pull-up resistor 29 for pulling up the bus 50 to the voltage of the power line 40;
A resistance control circuit 30 for controlling the connection between the pull-up resistor 29 and the bus 50;
A clock oscillation circuit 20;
A controller 23 for controlling a voltage supplied by the regulator 21 based on an interface voltage switching command from the electronic device 1;
When the controller 23 receives the interface voltage switching command and performs control to switch the output voltage of the regulator 21, the interface voltage of the electronic device 1 is normally switched to the voltage range designated by the controller 23 based on the output of the detection circuit 18. A stabilization wait circuit 25 for determining whether or not the buffers 26 to 28 have shifted to a stable operable state;
When the controller 23 receives the interface voltage switching command and performs control to switch the output voltage of the regulator 21, means for notifying the electronic device 1 of the interface voltage switching state of the electronic device 2 from the input / output buffer 26 via the bus 51. An output control circuit 24 having
Consists of

  Here, the resistance control circuit 30 that controls the pull-up resistor 29 can be controlled by a command from the electronic device 1 via the controller 23.

  Further, the controller 23 and the output control circuit 24 in the electronic device 2 operate in synchronization with either or both of the clock supplied from the electronic device 1 via the bus 52 and the clock supplied from the oscillation circuit 20 of the electronic device 2. Execute.

  In the communication system according to the first embodiment of the present invention, the buffers 16 to 18 of the electronic device 1 and the buffers 26 to 28 of the electronic device 2 operate at the first voltage when the power is turned on.

In the communication system having the above configuration, when the first voltage generated by the voltage source 10 is higher than the second voltage generated by the regulator 11 included in the electronic device 1 and the regulator 21 included in the electronic device 2. The procedure for switching the interface voltage between the electronic device 1 and the electronic device 2 will be described below.

  First, in the communication system according to the first embodiment of the present invention shown in FIG. 1, a procedure for lowering the interface voltage between the electronic device 1 and the electronic device 2, that is, a procedure for switching from the first voltage to the second voltage. This will be described with reference to the sequence diagram of FIG.

In FIG.
In the communication system between the electronic device 1 and the electronic device 2 in which the interface voltage is operating at the first voltage, the controller 13 of the electronic device 1 switches the interface voltage between the electronic device 1 and the electronic device 2 to the second voltage. Is issued from the output control circuit 17 to the electronic device 2 via the bus 51 (SH2-1).

  When the controller 23 of the electronic device 2 receives the command for switching to the second interface voltage from the electronic device 1 via the bus 51, if the command is received without error, a response is returned to the electronic device 1 (SS2). -1) A status indicating whether or not the buffers 26 to 28 of the electronic device 2 are operable at the second voltage specified by the electronic device 1 is returned to the electronic device 1 (SS2-2). The status may include information such as current consumption when the buffers 26 to 28 of the electronic device 2 operate at the second voltage.

  After that, when the buffers 26 to 28 of the electronic device 2 can operate at the second voltage (SS2-3), the controller 23 controls the output control circuit 24 when the pull-up resistor 29 is not connected to the bus 50. Then, an instruction to connect the pull-up resistor 29 to the bus 50 is issued. Further, the output control circuit 24 is instructed to control the resistance control circuit 30 to connect the bus 50 to the first voltage which is the voltage of the power supply line 40 via the pull-up resistor 29 (SS2-4, SS2). -5).

  When the electronic device 2 is driving the bus 50 by the input / output buffer 26, the output control circuit 24 controls the input / output buffer 26 and releases the drive of the bus 50 (Hi-Z) (SS2-6). , SS2-7).

  Subsequently, the controller 23 performs control to switch the output voltage of the regulator 21 from the first voltage to the second voltage (SS2-8).

  Further, the controller 23 instructs the stabilization wait circuit 25 to wait for the stabilization of the interface voltage of the electronic device 2, and the stabilization wait circuit 25 determines the interface voltage based on the determination of the detection circuit 24 that detects the output voltage of the regulator 21. When the switching is completed, it is determined whether or not the buffers 26 to 28 of the electronic device 2 have stably shifted to a state in which operation is possible with the second voltage (SS2-9). 24 is notified that the interface voltage of the electronic device 2 has been switched normally.

  When the stabilization wait circuit 25 notifies the output control circuit 24 that the interface voltage of the electronic device 2 has been switched normally, the output control circuit 24 outputs an L level to the bus 50 via the first input / output buffer 26 ( SS2-10). Since the bus 50 is maintained at the H level based on the first voltage supplied from the power line 40 by the pull-up 22 until this step, this step is performed for the electronic device 1 via the bus 50. It is notified as a signal change from the H level to the L level based on one voltage level.

Finally, the output control circuit 24 controls the resistance control circuit 30 to disconnect the bus 50 and the pull-up 29 (SS2-11). As a result, the first input / output buffer 26 can stably input / output an H level or L level signal based on the second voltage level to the bus 50.

  Note that, in the interface voltage switching control of the electronic device 2 described above, the controller 23 and the output control circuit 24 operate with the clock of the oscillation circuit 20 from SS2-4 to SS2-8.

  If the second voltage instructed by the electronic device 1 at SS2-3 is outside the operation range of the electronic device 2, the electronic device 2 ends the voltage interface switching control without performing the subsequent operations. To do.

  On the other hand, the electronic device 1 that has issued a command to switch the interface voltage between the electronic device 1 and the electronic device 2 to the electronic device 2 in SH2-1, the response returned from the electronic device 2 in SS2-1 and the electronic device in SS2-2. When the status returned from the device 2 is received, if the response and status are normal and the buffers 26 to 28 of the electronic device 2 are operable at the second voltage (SH2-2), the interface voltage of the electronic device 2 After a clock having a specific number of cycles necessary for switching is supplied to the electronic device 2, the clock is stopped (SH2-3). In addition, when there is an abnormality in the response or status in SH2-2, or when the buffers 26 to 28 of the electronic device 2 cannot operate at the second voltage, the voltage interface switching control is terminated without performing the subsequent operations. To do.

  In the abnormality process when there is an abnormality in the response or status, the power of the electronic device 2 is turned on again (power cycle), and the buffers 16 to 18 of the electronic device 1 and the buffer 26 of the electronic device 2 are used with the first voltage. To establish communication of the communication system.

  After the clock is stopped at SH2-3, the electronic device 1 waits for the interface voltage switching processing of the electronic device 1 until the interface voltage switching of the electronic device 2 is completed, that is, the L level is detected by the bus 50 (SH2-4). ). However, when the switching of the interface voltage from the electronic device 2 is not completed within the preset waiting time (SH2-5), the electronic device 1 performs the abnormality process without performing the subsequent operations (SH2-11). ). This abnormality process is the same as the process performed when there is an abnormality in the response or status in SH2-2.

In SH2-4, when it is detected that the switching of the interface voltage of the electronic device 2 has been completed and the voltage of the bus 50 has become L level, the controller 13 of the electronic device 1
The regulator 11 is controlled to switch the output voltage from the first voltage to the second voltage (SH2-6).

  Further, the controller 13 instructs the stabilization wait circuit 15 to wait for the stabilization of the interface voltage of the electronic device 1, and the stabilization wait circuit 15 determines the interface voltage based on the determination of the detection circuit 14 that detects the output voltage of the regulator 11. When the switching is completed and the buffers 16 to 18 of the electronic device 1 are stably shifted to a state where they can operate at the second voltage (SH2-7), and when it is determined that the switching is completed, the output control circuit 14 is notified that the interface voltage of the electronic device 1 has been switched normally.

  Then, the output control circuit 14 restarts the clock to the electronic device 2 via the output buffer 18 via the bus 52 (SH2-8), and notifies the electronic device 2 that the switching of the interface voltage of the electronic device 1 has been normally completed. The Ack signal to be output is output to the bus 51 (SH2-9), and the interface voltage switching control of the electronic device 1 is completed (SH2-10).

  Here, instead of the electronic device 1 explicitly notifying the electronic device 2 of the switching of the interface voltage using the Ack signal, the electronic device 2 detects the restart of the clock in SH2-8, and the electronic device 1 It is also possible to determine completion of switching of the interface voltage.

  Finally, the electronic device 2 determines switching of the interface voltage of the electronic device 1 by the Ack signal indicating completion of switching of the interface voltage from the electronic device 1 or by restarting the clock (SS2-12), and the bus is passed through the output buffer 26. After outputting the H level to 50 (SH2-13), the output to the bus 50 is released (Hi-Z is assumed) (SS2-14), so that the electronic device 1 and the electronic device 2 of this communication system are connected. The procedure for switching the interface voltage from the first voltage to the second voltage is completed (SS2-15).

  FIG. 3 is a timing chart showing the operations of the buses 50, 51 and 52 in the sequence of FIG. In FIG. 3, “CMD” is an interface voltage switching command issued by the electronic device 1, “CMD” is a response returned by the electronic device 2, “Status” is a status returned by the electronic device, and “H” is an H level output. State, “L” is a state where an L level is output, “Z” is that no signal is output from either the electronic device 1 or the electronic device 2, and the bus is fixed to the interface voltage via a pull-up resistor. Indicates the state. In FIG. 3, the Ack signal in step SH2-9 in FIG. 2 is realized by “L” output in one cycle.

Next, in the communication system according to the first embodiment of the present invention shown in FIG. 1, the procedure for switching the interface voltage between the electronic device 1 and the electronic device 2 from the second voltage to the first voltage is shown in the sequence diagram of FIG. Will be described.
In FIG.
In the communication system between the electronic device 1 and the electronic device 2 in which the interface voltage is operating at the second voltage, the controller 13 of the electronic device 1 switches the interface voltage between the electronic device 1 and the electronic device 2 to the first voltage. Is issued from the output control circuit 17 to the electronic device 2 via the bus 51 (SH4-1).

  When the command to switch to the first voltage of the interface voltage from the electronic device 1 is received via the bus 51, the controller 23 of the electronic device 2 returns a response to the electronic device 1 when receiving the command without error (SS4). -1) A status including information indicating whether or not the buffers 26 to 28 of the electronic device 2 are operable at the first voltage instructed by the electronic device 1 is returned to the electronic device 1 (SS4-2).

  Thereafter, when the buffers 26 to 28 of the electronic device 2 are operable at the second voltage (SS4-3), the output control circuit 24 controls the input / output buffer 26 based on an instruction from the controller 23, and outputs the signal to the bus 50. A level signal is output (SS4-4).

  On the other hand, the electronic device 1 that has issued a command to switch the interface voltage between the electronic device 1 and the electronic device 2 to the electronic device 2 in SH4-1, the response returned from the electronic device 2 in SS4-1, and SS4-2. The status returned from the electronic device 2 is confirmed, and if the response and status are normal (SH4-2), a clock having a specific number of cycles necessary for switching the interface voltage of the electronic device 2 is supplied to the electronic device 2. After that, the clock is stopped (SH4-3). If the response or status is abnormal in SH4-2, the voltage interface switching control is terminated without performing the subsequent operations.

  In the abnormality process when the response or status is abnormal, the communication of the communication system is established by operating the buffers 16 to 18 and the buffers 26 to 28 with the first voltage after performing the power cycle as described above. To do.

  After the clock is stopped at SH4-3, the output control circuit 14 outputs an H level to the bus 51 via the input / output buffer 17 (SH4-4), controls the regulator 11, and sets the output voltage of the regulator to the second voltage. The voltage is switched to the first voltage (SH4-5).

  Further, the controller 13 instructs the stabilization wait circuit 15 to wait for the stabilization of the interface voltage of the electronic device 1, and the stabilization wait circuit 15 determines the interface voltage based on the determination of the detection circuit 14 that detects the output voltage of the regulator 11. When the switching is completed, it is determined whether or not the buffers 16 to 18 of the electronic device 1 have stably shifted to a state in which they can operate at the first voltage (SH4-6). The circuit 14 is notified that the interface voltage of the electronic device 1 has been switched normally. The output control circuit 14 outputs the bus 51 to the L level via the input / output buffer 17, thereby notifying that the interface voltage of the electronic device 1 has been switched normally. (SH4-7). In steps up to SH4-6, the bus 51 is kept at the H level with a voltage equal to or higher than the second voltage.

When detecting that the L level is output to the bus 51 (SS4-5), the controller 23 controls the output voltage of the regulator 21 to be switched to the first voltage (SS4-6). Further, the controller 23 instructs the stabilization wait circuit 25 to wait for stabilization of the interface voltage of the electronic device 2, and the stabilization wait circuit 25 determines the interface voltage based on the determination of the detection circuit 24 that detects the output voltage of the regulator 21. It is determined whether or not the switching has been completed and the buffers 26 to 28 of the electronic device 2 have stably shifted to a state operable with the first voltage (SS4-7). If it is determined that the switching has been completed, the output control circuit 24 is notified that the interface voltage of the electronic device 2 has been switched normally.
When notified from the stabilization wait circuit 25 that the interface voltage of the electronic device 2 has been switched normally, the output control circuit 29 outputs an H level to the bus 50 via the input / output buffer 26 (SS4-8). From SS4-4 to this step, the electronic device 2 outputs an L level to the bus 50. In SS4-8, the electronic device 1 is based on the first voltage level from the L level via the bus 50. A signal change to the H level is notified.
The electronic device 1 waits for the interface voltage switching processing of the electronic device 1 until the interface voltage switching of the electronic device 2 is completed, that is, until the H level is output to the bus 50 (SH4-8). However, when the switching of the interface voltage from the electronic device 2 is not completed within the preset waiting time (SH4-9), the electronic device 1 performs the abnormality process without performing the subsequent operation (SH4-13). ). This abnormality process is the same as the abnormality process performed when there is an abnormality in the response or status in SH4-2.

When the switching of the interface voltage of the electronic device 2 is completed and the H level is output to the bus 50 in SH4-8, the controller 13 of the electronic device 1
Using the output control circuit 14, the clock supply to the electronic device 2 is resumed by the bus 52 via the output buffer 18 (SH4-10), and the interface voltage switching of the electronic device 1 to the electronic device 2 has been normally completed. Is notified by the Ack signal (SH4-11), and the switching control of the interface voltage of the electronic device 1 is completed (SH4-12).

  Here, instead of explicitly notifying the electronic device 2 of the switching of the interface voltage using the Ack signal, the electronic device 1 detects the resumption of clock supply in SH4-10, and the electronic device 1 It is also possible to determine the completion of switching of the interface voltage.

Finally, the electronic device 2 detects the switching of the interface voltage of the electronic device 1 by detecting the Ack signal indicating completion of switching of the interface voltage from the electronic device 1 or the restart of the clock supply (SS4-9), and the output to the bus 50 (Hi-Z) (SS2-1)
0), the procedure for switching the interface voltage between the electronic device 1 and the electronic device 2 of the communication system from the second voltage to the first voltage is completed (SS4-11).

Here, the operation of the buses 50, 51 and 52 in the sequence of FIG. 4 is shown in a timing chart of FIG. In FIG. 5, “CMD”, “RES”, “Status”, “H”, “L”, and “Z” mean the same state as in FIG.
(Second Embodiment)
FIG. 6 is a diagram illustrating a circuit configuration example of a communication system according to the second embodiment of the present invention.

  In FIG. 6, the pull-up resistor 31 connects the regulator 11 and the bus 50. The other components of FIG. 6 are the same as those of the communication system according to the first embodiment described in FIG.

  Here, in the communication system according to the second embodiment of the present invention, a procedure for lowering the interface voltage between the electronic device 1 and the electronic device 2, that is, a procedure for switching from the first voltage to the second voltage is shown in FIG. Will be described.

  In FIG. 7, control procedures SH7-1 to 11 of the electronic device 1 are procedures equivalent to the control procedures SH2-1 to 11 in the communication system according to the first embodiment in the sequence diagram 2, respectively. Further, the control procedures SS7-1 to 3, 6 to 10 and 12 to 15 of the electronic device 2 are respectively controlled by the communication procedures SS2-1 to SS3 and 6 to 10 in the communication system according to the first embodiment in the sequence diagram 2. , 12-15. In other words, in the communication system according to the second embodiment, the steps (SS2-3, SS2-4, SS2-4, SS2-4, control, etc.) inside the electronic device 2 performed in the communication system according to the first embodiment. And SS2-11) are not implemented, but the bus 50 has the bus released by the first input / output buffer 16 in the electronic device 1 and the first input / output buffer 26 in the electronic device 2 by the pull-up resistor 31. In the case (= Hi-Z state), the voltage supplied from the regulator 11 of the electronic device 1, that is, the interface voltage of the electronic device 1 is always maintained at the H level, and the same effect as the communication system according to the first embodiment is achieved. It is possible to obtain

  Next, in the communication system according to the second embodiment of the present invention, the procedure for increasing the interface voltage between the electronic device 1 and the electronic device 2, that is, the procedure for switching from the second voltage to the first voltage is shown in FIG. This will be described with reference to a sequence diagram.

  In FIG. 8, control procedures SH8-1 to 10 and 12 of the electronic device 1 are the same as the control procedures SH4-1 to 10 and 12 in the communication system according to the first embodiment in the sequence diagram 4 respectively. is there. Further, the control procedures SS8-1 to 7 and 11 of the electronic device 2 are procedures equivalent to the control procedures SS4-1 to 7 and 11 in the communication system according to the first embodiment in the sequence diagram 4 respectively. Here, in the communication system according to the second embodiment, after the interface voltage switching of the electronic device 2 is completed (SS8-7), the output control circuit 24 releases the output of the input / output buffer 26 (= Hi-Z state). ) And complete the switching. That is, the bus 50 is opened before the clock supply from the electronic device 1 is resumed (SH8-10). The bus 50 is connected to the voltage supplied from the regulator 11 of the electronic device 1, that is, the H in the interface voltage of the electronic device 1. The level is maintained, and it is possible to obtain the same effect as that of the communication system according to the first embodiment. Here, the electronic device 1 opens the bus 51 after restarting the clock supply, and completes the switching of the interface voltage (SH8-11).

  Here, the operations of the buses 50, 51, and 52 in the sequence of FIG. 8 are shown in a timing chart of FIG. In FIG. 9, “CMD”, “RES”, “Status”, “H”, and “L” Z ”mean the same state as in FIG.

  In the block configuration diagrams (FIGS. 1 and 6) for explaining the communication systems according to the first and second embodiments of the present invention, only elements related to the interface circuit according to the present invention are shown. Elements relating to the operation of other communication systems unrelated to the invention are not shown.

  In the first and second embodiments, the regulator 11 of the electronic device 1 outputs the first voltage supplied from the voltage source 10 or the second voltage generated from the first voltage. However, the present invention is not limited to this, and an output voltage can be selected from voltages from a plurality of voltage sources and a plurality of generated voltages. Similarly, the regulator 21 also outputs the first voltage supplied from the power line 40 or the second voltage generated from the first voltage to the electronic device 2, but the present invention is not limited to this, and the voltage from a plurality of voltage sources is output. It is also possible to select an output voltage from a plurality of generated voltages. As described above, in the configuration in which the interface voltage can be selected from a plurality of voltages without being limited to the first voltage and the second voltage, means capable of confirming the interface voltage range that can be operated between the electronic device 1 and the electronic device 2 respectively. And a means for issuing an instruction to instruct which voltage to set when issuing an interface voltage switching instruction from the electronic device 1, and at the start-up stage of the communication system, It is necessary to operate with a first power source supplied from a specific voltage source 10 between the electronic devices 2.

  Further, the bus configuration between the electronic device 1 and the electronic device 2 need not be limited to the block configuration (FIGS. 1 and 6) detailed in the communication systems according to the first and second embodiments. In a system that transmits and receives data, a clock (output buffer 18, input buffer 28, and bus 52) is not required. Further, in the timing charts (FIGS. 3, 5, and 9) in the first or second embodiment, the bus 50 transmits and receives commands and transmits the interface voltage switching state from the electronic device 1 to the electronic device 2. Thus, although the status transmission from the electronic device 2 to the electronic device 1 and the transmission of the interface voltage switching state are performed by the bus 51, it is not necessary to limit the number of buses to two, and the electronic device 1 and the electronic device If the function for transmitting the interface voltage switching state of 2 is independently assigned to the bus, there is no restriction on which of the two or more buses the remaining functions are assigned to.

  Further, there are voltage conditions that can be set by the electronic device 2 such as when the interface voltage that can be set is notified from the electronic device 2 to the electronic device 1 in advance, or when the interface voltage is returned to the initial interface voltage by the switching process of the interface voltage If it is obvious from the electronic device 1, it is not necessary for the electronic device 2 to issue a response and status in response to a command issued from the electronic device 1, and the electronic device 1 also receives a response and status from the electronic device 2. In the case of switching the interface voltage in the present invention without confirming that it is normal, the effect of the present invention does not change.

  In addition, it is obvious that an electronic device including the interface circuit according to the present invention is not limited to a removable device such as a memory card or an IO card. For example, a controller LSI, a memory, and other functional blocks are sealed in a single package. However, the present invention can be applied to LSI-shaped electronic devices used by soldering to a substrate.

According to the interface circuit, the electronic device including the interface circuit, the communication system, and the voltage switching method according to the present invention, the slave device switches the interface voltage of the slave device in response to the interface voltage change command from the host device. After that, when notifying the completion of voltage switching to the host device, communication at the signal level based on the voltage on the host device interface side is always possible, so the interface voltage switching control is more reliable than in the conventional technology. In a system that can be executed and can select an operating voltage from a plurality of interface voltages, at least two or more existing interface standards during operation of a host device and a slave device are stable and efficient with the same number of buses. Turn off the interface voltage It can be obtained to become.

The block diagram which shows the structure of the communication system which concerns on the 1st Embodiment of this invention. 1 is a sequence diagram showing a procedure for lowering the interface voltage between the electronic device 1 and the electronic device 2 in the communication system of FIG. 2 is a timing chart showing the movement of the buses 50, 51 and 52 in the sequence of FIG. 1 is a sequence diagram showing a procedure for increasing the interface voltage between the electronic device 1 and the electronic device 2 in the communication system of FIG. 4 is a timing chart showing the movement of the buses 50, 51, and 52 in the sequence of FIG. The block diagram which shows the structure of the communication system which concerns on the 2nd Embodiment of this invention. 6 is a sequence diagram showing a procedure for lowering the interface voltage between the electronic device 1 and the electronic device 2 in the communication system of FIG. 6 is a sequence diagram showing a procedure for increasing the interface voltage between the electronic device 1 and the electronic device 2 in the communication system of FIG. Timing chart showing the movement of the buses 50, 51, 52 in the sequence of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Host side electronic device 2 ... Slave side electronic device 10 ... Voltage source 11, 21 ... Regulator 12, 22 ... Voltage detection circuit 13, 23 ... Controller 14, 24 ... Output control circuits 15, 25 ... Stabilization wait circuits 16, 17, 26, 27 ... I / O buffer 18 ... Output buffer 28 ... Input buffers 19, 29 ... Pull-up resistor 30 ... Pull-up resistance control circuit 40: power supply lines 50, 51 ... communication bus 52 ... clock bus

Claims (14)

A communication system in which at least one of the at least two electronic devices serves as a host device between at least two electronic devices, and performs master-slave communication with at least one slave device of the at least two electronic devices. An interface circuit provided in the slave device,
The interface circuit is
Means for continuously outputting the H level at the voltage level before switching to the host device during the interface voltage switching of the slave device when lowering the interface voltage between the host device and the slave device;
Means for outputting an L level after completion of switching of the interface voltage of the slave device.   2. The interface circuit according to claim 1, further comprising means for using a pull-up resistor connected to the host-side power supply for maintaining the voltage level before switching.   3. The interface circuit according to claim 2, further comprising means for disconnecting the pull-up resistor after completion of voltage switching.   An electronic device comprising the interface circuit according to claim 1. A communication system in which at least one of the at least two electronic devices serves as a host device between at least two electronic devices, and performs master-slave communication with at least one slave device of the at least two electronic devices. An interface circuit provided in the host device,
The interface circuit is
Means for detecting completion of interface voltage switching of the slave device when lowering the interface voltage between the host device and the slave device;
Means for switching the interface voltage of the host device after completion of the interface voltage switching of the slave device;
An interface circuit characterized by comprising:   An electronic device comprising the interface circuit according to claim 5.   A communication system comprising: the electronic device according to claim 4; and the electronic device according to claim 6. A communication system in which at least one of the at least two electronic devices serves as a host device between at least two electronic devices, and performs master-slave communication with at least one slave device of the at least two electronic devices. In reducing the interface voltage between the host device and the slave device in
During the interface voltage switching of the slave device, the slave device continues to output H level at the voltage level before switching from the slave device to the host device;
Outputting L level from the slave device to the host device after completion of interface voltage switching of the slave device;
Detecting the L level from the slave device and switching the interface voltage of the host device. A communication system in which at least one of the at least two electronic devices serves as a host device between at least two electronic devices, and performs master-slave communication with at least one slave device of the at least two electronic devices. An interface circuit provided in the host device,
The interface circuit is
Means for continuously outputting an H level at a level equal to or higher than the voltage before switching to the slave device during the interface voltage switching of the host device when raising the interface voltage between the host device and the slave device;
Means for outputting L level after completion of interface voltage switching of the host device;
An interface circuit characterized by comprising:   An electronic device comprising the interface circuit according to claim 9. A communication system in which at least one of the at least two electronic devices serves as a host device between at least two electronic devices, and performs master-slave communication with at least one slave device of the at least two electronic devices. An interface circuit provided in the slave device,
The interface circuit is
Means for outputting an L level during switching of the interface voltage of the host device when raising the interface voltage between the host device and the slave device;
Means for detecting completion of interface voltage switching of the host device and means for switching interface voltage of the slave device after completion of interface voltage switching of the host device;
Means for outputting an H level at the voltage level after switching after completion of the interface voltage switching of the slave device;
An interface circuit characterized by comprising:   An electronic apparatus comprising the interface according to claim 11.   A communication system comprising the electronic device according to claim 10 and the electronic device according to claim 11. A communication system in which at least one of the at least two electronic devices serves as a host device between at least two electronic devices, and performs master-slave communication with at least one slave device of the at least two electronic devices. In raising the interface voltage between the host device and the slave device in
Outputting an L level from the slave device during switching of the interface voltage of the host device;
Continuing to output H level from the host device to the slave device at a level equal to or higher than the voltage before switching;
Outputting L level to the slave device after completion of interface voltage switching of the host device;
Detecting L level from the host device and switching the interface voltage of the slave device;
And a step of outputting an H level at the voltage level after switching after the interface voltage of the slave device has been switched.

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