JPS6214245A - One-chip microcomputer - Google Patents

Abstract

PURPOSE:To improve the availability of the port of microcomputer by controlling the port to use all periods not used to send the address concerning the port shared by the time division. CONSTITUTION:Concerning a port 52 which is used to send the signal for designating the address and is not necessary to use to input the instruction sentence read from an external ROM 2 by said address, out of the whole time except the time necessary to sent the signal for designating the address, the time as much as possible can be used to input and output the signal from an external circuit 3. Thus, the same effect as the case that the port used for the data input/output at the section of the external circuit 3 is increased can be obtained.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention relates to a one-chip microcomputer (hereinafter abbreviated as microcomputer), and in particular, the present invention relates to a one-chip microcomputer (hereinafter abbreviated as microcomputer), and in particular, the present invention relates to a one-chip microcomputer (hereinafter abbreviated as microcomputer), and in particular,
This is related to the microcomputer stored in the OM.

[Conventional technology]

Figure 3 is a block diagram showing the input/output signal relationship of a conventional microcomputer.
M, +31Vi This is an external circuit that inputs and outputs data to and from the microcomputer (1). By the way, the microcomputer (1
) Because the number of external data input/output terminals (hereinafter also referred to as ports) should be kept as small as possible due to its structure, it is common to use one terminal for multiple purposes on a time-sharing basis. In FIG. 3, the I10 port (meaning I10Vi input/output) indicated by (4) is a port dedicated to data input/output with the external circuit (3), and the part indicated by (5) is a port dedicated to data input/output with the external circuit (3).
It is used by switching to address output to 21, input of instructions read from the program stored in external ROM 21, and data input/output to external circuit (3) (represented as port input and port output in Figure 3). It is a port that

Figure 4 is a block circuit showing such port switching, where (10) is a register, (11) is a latch, and (12)
The Vi control transistor (13) is a terminal. When outputting data from the terminal (13) to the outside, use the register (
Latch the data in 10) into the latch (11),
Transistor (12)'! z control (1 in the data
(only bits are representatively shown), the contents of the latch (11) are output to the terminal (13). Also, when external data is input from the terminal (13), it is interrupted between the latch (11) and the terminal (13) by the transistor (12), and the terminal (
13) to write external data to register (10).

In Figure 3, external ROM +21 has a microcomputer (1)
If a circuit is provided to fetch the address output from the microcontroller (1), there will be a port that outputs the address signal for accessing the external ROM +21 from the microcontroller (1), and a port that outputs the address signal for accessing the external ROM +21 from the microcontroller (1), and a port that outputs the address signal that is read from the program memory of the external ROM +21 in response to this address signal. The same port as the port for inputting instructions to the microcomputer (1) can be used on a time-sharing basis.

Further, this same port can be used as a port for executing read instructions and outputting data from the microcomputer (1) to the external circuit (3).

By the way, the number of bits of the address signal for accessing the external ROM +21 and the number of bits of the instruction statement read from the external ROM +21 by that address signal are different, and generally the number of bits of the address signal is larger. many. Therefore, when the ports indicated by reference numeral (5) in FIG. 3 are used in a time-sharing manner, two types of ports exist. The first type of port has three ports: one for sending an address signal (that is, for specifying an address), one for inputting a command corresponding to the address signal, and one for inputting and outputting data to the external circuit (3) (that is, for port input/output). The second type of port is a port whose operations are repeated in a time-sharing manner, and the second type of port is a port where only two operations, one for addressing and one for port input/output, are repeated.

FIG. 5 is an operation time chart showing time division of ports in a conventional device, and FIG. FIG. 5 la is a time chart for the second type of port (that is, a case where one port inputs and outputs two types of signals by time division). It is needless to say that output for address designation must be performed at the same time in both ports operating as shown in FIG. 5 1al and ports operating as shown in FIG. 1bl. In the conventional time division shown in Figure 5, even in the ports shown in Figure 5+b), ports that do not need to be used for command input in the phase corresponding to command input are used for port rafting. The port used for command input is (Fig. 5 fa).
Reference) When the instruction input is terminated and used as input/output (for port input/output) to the external circuit (3), the microcontroller (1) is also configured to be used for port input/output in Figure 5 [bl]. The switch for the port was activated.

[Problem that the invention seeks to solve]

Since port switching in conventional microcontrollers is performed as described above, the second type of port, which only needs to input and output two types of signals, as shown in FIG. As shown in the hatched area on the left edge of the port, there is a time when the port is being used for a long time, which caused the problem of poor port utilization.0 As shown in Figure 3 as I10 port (4) Providing a large number of ports dedicated to input/output from the external circuit (3) is difficult to achieve with a microcontroller with a small number of pins, and the port used for addressing the external ROM should be used as effectively as possible by time-sharing. When a port is used for input/output, there are times when the port is left floating during time sharing, which is a problem that should be improved.

This invention was made to solve the above-mentioned problems, and the overall purpose is to provide a microcontroller that can be effectively used for sending out address signals for accessing external ROM and for inputting and outputting data to external circuits. It is said that

[Means for solving problems]

In the present invention, a second type of port, which is used for sending an address designation signal, but does not need to be used for inputting an instruction statement read from an external ROM by the address, is described. , out of all the time other than the time required for sending signals for address specification, as much time as possible can be used for inputting and outputting signals from external circuits.

[Effect]

Since a port that can be used for data input/output with an external circuit for a longer period of time than conventional time division is obtained, the same effect as that obtained by adding a port used for data input/output with an external circuit can be obtained.

〔Example〕

All drawings of embodiments of this invention will be described below.

FIG. 1 is a block diagram showing one embodiment of the present invention;
The same reference numerals as in the figure indicate the same or equivalent parts, (5o) is a port where address output, command input, and port output are performed, (51) it is a port where address output, command input, and port input are performed), (52) is a port where address output and port input/output are performed.

FIG. 2 is an operation time chart showing the time division of ports in the device of the present invention, and is displayed using the same method as FIG. 5. Figure 2 fal is the same as Figure 5 fat, Figure 2 fbl is the left end of Figure 5 tbl, and the time when the port is in a floating state is switched so that the time in Figure 2 tb+ is used for port input/output. ing.

The time division time for port input/output in FIG. 2 fbl is 2μ8ee when the machine cycle is 4μ8ee. Consider a case where the first 1 .mu.sec of these 2 .mu.sec is used for data output, and the latter 1 .mu.sec is used for data input by switching with a circuit as shown in FIG. 500 nsec is sufficient for the data output from the microcomputer (1) to be latched by the external circuit (3), and 1 μsec is sufficient for inputting data from the external circuit (3) to the microcomputer (1). Therefore, the same effect can be obtained by doubling the number of ports by using the port input/output time shown in FIG. 2 [bl for both port input and output.

In the above embodiment, the time-sharing order of the ports is command input, port input/output, and address specification output, but this order may be port input/output, command input, and address specification output.

〔Effect of the invention〕

As described above, according to the present invention, in a microcomputer that reads a program from an external ROM and executes it, the address is Since the entire period not used for signal transmission is controlled so that it can be used for data input/output to external circuits, the utilization rate of the microcomputer ports can be improved.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is an operation time chart showing port time division in the device shown in FIG. 1, FIG. 3 is a block diagram showing a conventional device, and FIG. 4 5 is a block diagram showing port switching, and FIG. 5 is an operation time chart showing time division of ports in the device of FIG. 3. (1) f′i microcomputer, (2) external pigeon, (3) external circuit, (50), (51) Fi first type port, (
52) t:1 second type of port. Note that the same reference numerals in each figure indicate the same or corresponding parts.

Claims (1)

[Claims] A one-chip microcomputer that reads and executes a program stored in an external ROM,
A first circuit which is shared by time sharing for the output of an address signal for accessing M, the input of a program command statement read from the external ROM by the address signal, and the input/output of data to an external circuit other than the external ROM. and a second type of port that is shared by time sharing only for the output of the address signal and the input/output of data to the external circuit, and in the time sharing of the second type of port. A one-chip microcomputer characterized in that the one-chip microcomputer is controlled so that all time other than the time required for outputting address signals can be used for inputting and outputting data to the external circuit.