JPH0535914B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a microcomputer (hereinafter referred to as a microcomputer) having a built-in input/output port for interfacing with peripheral equipment.

[Conventional technology]

Conventionally, this type of microcomputer has been equipped with a mode register 2 for switching input and output of a port circuit 1 for interfacing with external equipment, as shown in FIG. Assume now that the mode register 2 is set so that the port circuit 1 functions as an input port. Here, when data that sets port circuit 1 to output mode is transferred from CPU 4 to mode register 2 via internal data bus 3, port circuit 1 switches to output mode and functions as an output port. It becomes like this. Similarly, switching from output port to input port is as follows.
This is realized by transferring data for setting the port circuit 1 to the input mode from the CPU 4 to the mode register 2 via the internal data bus 3.

[Problem that the invention seeks to solve]

The conventional microcontrollers mentioned above are configured to switch the input/output mode of the input/output port by specifying the mode register controlled by the CPU, so the port is not enabled while the CPU is accessing the mode register. Especially in the case of a microcomputer that performs control such as switching port input/output frequently, there is a drawback that port usage efficiency becomes poor.

[Means for solving problems]

The microcomputer of the present invention includes a compare register, a comparator that compares data input/output to the input/output port and data set in the compare register, and is provided in the input/output port, and receives a match signal from the comparator. and means for switching the input/output mode of the input/output port when the input/output port is output.

In this way, by directly switching the input/output mode of a port depending on the output data to the port or the input data from the port, it is possible to control the port input/output, especially in microcontrollers that require control to frequently switch the input/output of the port. It can improve usage efficiency and reduce the burden on software.

[Example] Next, an example of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing one embodiment of a microcomputer according to the present invention. A port circuit 1 is configured by an AND gate 11, 3-state buffers 12, 13, a buffer 14, a port register 15, and transfer gates 16, 17.
Comparator 7, trigger flip-flop 21,
A control circuit for switching the input/output mode of the port circuit 1 is configured in the inverter 22.
The port circuit 1 is provided with an external terminal group 5 (8 bits). In this embodiment, input/output switching of the port circuit 1 is performed at the level of the external terminal group 5 of the port circuit 1. That is, port circuit 1
If the same data as the 8-bit data set in compare register 6 is output while the port circuit is set to output mode, port circuit 1 automatically switches to input mode and port circuit 1 is set as an input port. When the data input to the external terminal group 5 is the same as the 8-bit data set in the compare register 6, the port circuit 1 automatically switches to the output mode.

The operation of this embodiment will be described below with reference to the timing chart of FIG.

First, data “FF” is stored in compare register 6.
is set, port circuit 1 is in output mode,
At this time, the output of the trigger flip-flop 21
It is assumed that IOCNT is "0". Further, it is assumed that the read signal PRD of the port register 15 is always "0". Since the port circuit 1 is in the output mode, in synchronization with the write signal WR from the CPU 4, the data DO1, DO2, DO3 (the above data are other than "FF") are sent to the port register 15 and the three active states. It is output to the external terminal group 5 via the buffer 13. Here, if the next output data DO4 is "FF", the comparator 7 outputs INT as a coincidence signal, and the output IOCNT of the trigger flip-flop 21 is inverted and becomes "1". Then, the 3-state buffer 12 of the port circuit 1 becomes active, the 3-state buffer 13 becomes inactive, and the port circuit 1 is switched to the input mode. Comparator 7
The output signal INT also functions as an interrupt signal to the CPU 4, and serves to make the CPU 4 recognize that the port circuit 1 has entered the input mode. Now,
Port circuit 1 that became input mode in this way
is the data DI1, DI2, sent from the outside.
For DI3 (the above data are other than "FF"), the 3-state buffer 12 in the active state outputs data to the internal bus 3 in synchronization with the read signal RD from the CPU 4. Here, if the next input data DI4 is "FF", the comparator 7 outputs the interrupt signal INT again, controls to stop the read signal RD, and the output IOCNT of the trigger flip-flop 21 becomes "0". ”
The port circuit 1 enters the output mode. Since the read signal RD stops, DI4 (data "FF") is not taken into the internal bus 3. Also,
The interrupt signal INT also serves to make the CPU 4 recognize that the port circuit 1 has entered the output mode.
In this way, the input/output mode of the port circuit 1 is switched every time the same data as the data set in the compare register 6 is input or output. In this embodiment, since "FF" is set as comparison data in the compare register 6, valid data as input/output data is other than "FF". In other words, in the case of an 8-bit port like this embodiment, one of the 256 types of data must be reserved as data for input/output control. However, as described below, the effects of the present invention can be fully achieved by interfacing microcomputers having the same port configuration as that of this embodiment.

FIG. 3 is a diagram showing an example of the use of the microcontroller shown in FIG.
P2, and external terminal group T of ports P1 and P2
1 and T2 are connected to each other. It is assumed that data "FF" is set in each compare register. Also, port P of microcomputer M1
1 is set to output mode, and port P2 of microcomputer M2 is set to input mode. That is,
Consider a case where data is transferred from microcomputer M1 to microcomputer M2. Here, microcomputer M1
Data “FF” from port P1 to external terminal group T1
Suppose that is sent. This means the end of data output from the microcomputer M1 to the microcomputer M2. Through this operation, port P1 of microcomputer M1 is quickly switched from output mode to input mode, port P2 of microcomputer M2 is quickly switched from input mode to output mode, and data can now be transferred from microcomputer M2 to microcomputer M1. It becomes like this. Comparing the above operations with the conventional example, we can see that the port P1 of the microcomputer M1, which is initially in output mode, outputs "FF" and switches to input mode. It appears to be equivalent to accessing the mode register of a port in the port and switching the port to the input state. but,
During the period when the control data “FF” is output from the port (corresponding to DO4 in Figure 2), the interrupt signal (second
(corresponding to INT in the figure) is occurring for only a short period of time, which is extremely short compared to the time required for the CPU to switch the mode register of the port as in the past. In other words, the period during which a port cannot be used effectively due to input/output mode switching is gradually shortened compared to the conventional method. Furthermore, microcomputer M1
The data "FF" outputted from the port P1 of the microcomputer M2 also has the effect of switching the port P2 of the other microcomputer M2 to the input mode. Therefore, for port P2, the mode is switched directly at the pin level, and it is no longer necessary to operate the mode register of microcomputer M2 via the CPU in order to set port P2 to input mode as in the past. This enables high-speed switching.

Although this example describes an 8-bit input/output port, there is no particular restriction on the number of bits of the port to be controlled, and the number of bits of the data compared by the comparator is also the same as the number of bits of the port. There's no need. For example, only the data input to or output from the lower 4 bits of an 8-bit port may be subject to input/output switching.

〔Effect of the invention〕

As explained above, the present invention directly switches the input/output mode of a port depending on the output data to the port or the input data from the port.
Particularly in microcomputers that require control to directly switch port input/output modes, this has the effect of increasing port usage efficiency and reducing the burden on software.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of the microcomputer of the present invention, FIG. 2 is a timing chart for explaining FIG. 1, FIG. 3 is a diagram showing an example of use of the embodiment of FIG. 1, and FIG. The figure is a block diagram of a conventional microcomputer. 1...Port circuit, 2...Mode register, 3
...Internal bus, 4...CPU, 5...External terminal group,
6...Compare register, 7...Comparator,
11...And gate, 12,13...3 state buffer, 14...Buffer, 15...Port register, 16,17...Transfer gate,
21...Trigger flip-flop, 22...Inverter, M1, M2...Microcomputer, P1, P2...
...Ports of microcontrollers M1 and M2, T1, T2...
External terminal group for ports P1 and P2.

Claims (1)

[Claims] 1 In a microcomputer with a built-in input/output port, a compare register, a comparator that compares data input/output to the input/output port and data set in the compare register, and a comparator provided in the input/output port and configured to A microcomputer comprising means for switching the input/output mode of the input/output port when a match signal is output from the comparator.