JPH04117585A - Microcomuter - Google Patents

Abstract

PURPOSE:To make the adding of a buffer unnecessary when microcomputers more than two are connected by providing a buffer circuit between peripheral circuits and an input/output terminal and controlling the continuity of the buffer circuit corresponding to an external signal. CONSTITUTION:An incorporated peripheral 104 connected by a CPU block 102 and an internal bus 103 of a microcomputer 101 is inputted to a buffer 110. Then, an HZRQ signal 106 is inputted to a high impedance control part 109. Then, the high impedance control part 109 outputs a RQ signal to the buffer 110 and a BIU 111, makes the buffer 110 and the BIU be in a off condition and makes an input/output terminal be in a high impedance condition. Thus, even when the microcomputers more than two are connected to the bus of one system, it is unnecessary to put the buffer between the buses.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a microcomputer (hereinafter referred to as a microcomputer).
Regarding.

[Conventional technology]

Conventional microcontrollers did not have the ability to set all input and output terminals to high impedance. FIG. 7 is a block diagram of a conventional microcomputer without a high impedance function. As shown in the figure, a conventional microcomputer 301 has internal components such as a bus arbitration unit 308, a serial control unit 309, a timer control unit 310, an interconnected control unit 3113, and a DMA control unit 312. Contains peripheral peripherals other than the CPU. Since the input/output terminals of these peripherals do not pass through the bus interface unit BIU, they do not go into a high impedance state even when a hold is applied to the microcomputer.

For this reason, such conventional microcontrollers can be wired OR
When creating a system in which multiple terminals are connected, it is necessary to add a buffer between the terminals and the system bus so that they can be disconnected from the system bus for terminals that do not go into a high impedance state during hold. There wasn't.

[Problem to be solved by the invention]

The conventional microcomputers mentioned above do not have a high impedance function, so when two or more microcomputers are connected to a bus in one system, it is necessary to insert a buffer between them and the bus.

However, recent microcontrollers are increasingly equipped with a large number of input/output bins, and as a result, the number of buffers increases in proportion to the number of input/output bins. The problem has been that the printed circuit board becomes larger due to the increase in the number of buffers.

An object of the present invention is to provide a microcomputer that does not require additional buffers even when two or more microcomputers are connected.

[Means to solve the problem]

The microcomputer of the present invention is characterized by having a plurality of peripheral circuits, a buffer circuit provided between the peripheral circuits and input/output terminals, and a control circuit that controls conduction of the buffer circuit according to an external signal. shall be.

〔Example〕

Next, embodiments of the present invention will be described using the drawings. FIG. 1 is a block diagram showing one embodiment of the present invention. C.P.
A built-in peripheral 104 connected to the U block 102 by an internal bus 103 is input to a buffer 110 . The high impedance control unit 109 receives a request from the H2RQ signal terminal 106, controls the buffer 110, and puts the external input/output terminal in a high impedance state.

First, when the microcontroller is normally operating, the buffer 11
0 is in the on state, and the internal bus of the microcomputer and the external bus are connected.

When disconnecting the microcomputer from the system bus from this state, as shown in FIG. 2, first the H2RQ signal 1.6 is input to the high impedance control section 109. Then, the high impedance control unit 109 outputs an RQ signal to the buffer 110 and BIUll, and
0 and BIUll are turned off to put the input/output terminals in a high impedance state. At the same time, buffer 11
The H2AK signal 107 is activated by the acknowledge AK signal from 0 and BIUIII, indicating that the input/output terminal of the microcomputer has entered a high impedance state.

Conversely, when canceling the high impedance state, as shown in FIG.
At the same time, the H2AK signal 109 is turned on by the AK signal from the buffer 110 and BAUIll.
becomes inactive and releases the high-impedance state.

In this embodiment, as can be seen from the timing chart, the buffer 110 is turned off after the AK signal (ie, HLDAK signal) from BIUIII becomes valid. This enables high impedance control by bus arbitration of BIUIII.

Next, a second embodiment of the present invention will be described using the drawings. FIG. 4 is a block diagram showing this embodiment. In this embodiment, in order to simplify the high impedance control section,
High impedance control from the BIU 211 is not performed, and the buffer 210 is turned off when the H2RQ 206 is enabled.

First, when the microcontroller is normally operating, the buffer 21
0 is in the on state, and the internal bus of the microcomputer and the external bus are connected.

When disconnecting the microcomputer from the system bus from this state, first input the HZ RQ signal 206 to the high impedance control section 209, as shown in FIG. Then, the high impedance control unit 209 outputs the RQ signal to the buffer 210 and BItJ 211, turns off the buffer 210 and BIU 211, and puts the input/output terminals in a high impedance state. At the same time, the AK signal from the buffer 210 and BIU 211 causes H2A
The K signal 207 is made active to indicate that the input terminal of the microcomputer has entered a high impedance state.

Conversely, when canceling the high impedance state, the high impedance control section 209 makes the H2RQ signal 206 inactive as shown in FIG.
Turn off the Q signal, turn on the buffer 210 and BAU211, and at the same time turn off the buffer 210 and BAU211.
AK signal H2 from 211 makes the AK signal 209 inactive and releases the high impedance state.

〔Effect of the invention〕

As explained above, the present invention provides a microcomputer with a high impedance function, an H2RQ signal terminal, an H2RQ signal terminal,
By having an H2QK signal terminal, even when connecting two or more microcontrollers to one system bus, there is no need to insert a buffer between the buses, and the addition of buffers can reduce the cost of the entire system. This has the effect of preventing problems such as the board becoming larger.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention, FIGS. 2 and 3 are waveform diagrams showing the operation of FIG. 1, respectively, and FIG. 4 is a block diagram showing another embodiment of the present invention. 5 and 6 are waveform diagrams showing the operation of FIG. 4, respectively, and FIG. 7 is a block diagram showing a conventional example. 101.201...Microcomputer, 102,202...
Microcomputer internal CPU block, 103.203...Microcomputer internal bus, 104,204...Microcomputer built-in peripheral, 105,205...HLDRQ signal terminal, 106,206...H2RQ signal terminal, 107.2
07...H2AK signal terminal, 108°208...H
zDAK signal terminal, 109,209...Hi-Z control section, 110.210...BUFFERllll, 21
1... BIU, 112, 212... Built-in peripheral input/output terminal, 113, 213... System bus external to the microcontroller.

Claims (1)

[Claims] A microcomputer comprising a plurality of peripheral circuits, a buffer circuit provided between the peripheral circuits and input/output terminals, and a control circuit that controls conduction of the buffer circuits in accordance with an external signal.