JPS60175135A - Key scanning circuit - Google Patents

Abstract

PURPOSE:To omit a protection diode and to shorten reading time by connecting key switches between two I/O ports and switching both the ports alternately to use them as output and input terminals of a key scanning signal. CONSTITUTION:The 1st I/O ports AIO0-IO3 of a microcomputer 22 are connected to the 2nd I/O ports BIO4-IO7 like a 4X4 matrix, four bits of the port A are made active to output a key scanning signal and the port B is used as the input terminal to check the key scanning signal. When only one bit is active, four bits of the port B are made active and the key scanning signal is outputted from the port B and inputted from the port A to check the signal. Thus, the input state of the key switches can be read out only by repeating I/O twice.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a key scan circuit that can be used when inputting information to a microcomputer using a key switch.

The configuration of the conventional example and its problems are as follows: When using a key matrix for input to a microcomputer and determining the input by key scanning, the output port and input port of the microcomputer 1 are connected as shown in Figure 1. Key switch 6-21 between
are connected in a matrix. Then, from the output port, a key scan signal is output to activate only one of the output terminals, and the signal from the key switch at that time is input to the input port, which is equal to the number of output terminals of the output port. This is repeated, and when only one bit of the series of inputs is active, it is determined that the key switch corresponding to that bit has been pressed.

However, in the case of such a conventional circuit, switch 6
It is necessary to insert diodes 2 to 6 in series so that when two or more of the terminals 21 to 21 are pressed at the same time, there is no disconnection between the active (high level) terminal of the output port and other terminals.

In addition, since the states of key switches 6 to 21 cannot be read at once, in the case of Fig. 1, key switches 6 to 9, 1
It is necessary to repeat the key scan four times from 0 to 13, 14 to 17, and 18 to 21, and there is a drawback that it takes time to read.

OBJECTS OF THE INVENTION It is an object of the present invention to provide a key scan circuit that eliminates the conventional drawbacks as described above, does not require a protection diode, and can shorten the reading time.

Structure of the Invention In the present invention, the key scan input/output ports of a computer are alternately switched to output terminals and input terminals for key scan signals, and the key scan signal is first input from the first input/output port. The key scan signal is output from the second input/output port and inputted from the second input/output port, and then the key scan signal is outputted from the second input/output port and inputted from the first input/output port. Since the input/output ports are used bidirectionally, no diode is required, and high-speed key operation is possible.

DESCRIPTION OF THE EMBODIMENTS A key scan circuit according to an embodiment of the present invention will be described below with reference to the drawings.

Figure 2 shows its configuration. In the figure, key switch 2
3 to 38 are the first input/output ports of the microcomputer 22! 00~03 and second input/output port IO4~I
Connect to O7 in a 4x4 matrix.

FIG. 3 shows a flowchart of the key switch input reading operation. First, the first input/output capo) A (IO8
~■o3) 4 bits are active (for example, low level)
to output the key scan signal. Then, the second input/output port B (IO4 to 107) is used as an input terminal, and the bits activated by the key switch are checked. At this time, if no bit is active, it can be determined that no key switch has been pressed. Furthermore, if two or more bits are active, it can be determined that at least two or more switches are pressed.

When only 1 bit is active, for example, when only IO6 is active, the key switch 26°29.33.
37 is pressed, next, 4 bits of the second input/output port A) are activated and a key scan signal is output, and the second input/output port A is activated. Enter from.

At this time, if none of the bits are active, it can be determined that the key switch was released between input from the second input/output port B and input from the second input/output port A, and two or more bits are If it is active, it can be determined that two or more switches are pressed. When only one bit is active, if the key switch at the intersection of the previously active input/output port B line and the currently active input/output port A line is pressed. I can judge.

In this way, according to this key scan circuit, the input state from the key switch can be read at high speed by simply repeating input and output twice. Further, the protective diode that was conventionally required can be omitted, and the circuit can be simplified.

Effects of the Invention As described above, according to the present invention, the key matrix input/output ports of the microcomputer are alternately used as key scan signal input/output terminals, thereby eliminating the need for protective diodes. can be,
Moreover, even if the number of keys in the matrix increases, the input state of the key switch can be read by inputting and outputting the key scan signal only twice, so high-speed operation is possible.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a conventional key scan circuit, and FIG. 2 is a circuit diagram of a key scan circuit in an embodiment of the present invention.
FIG. 3 is a flowchart showing the operation. 22...Microcomputer, 23-38.
...Key button switch. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2

Claims (1)

[Claims] The first microcomputer. A key switch is connected between the second input/output boat, and the first input/output port is connected between the first and second input/output ports. A key scan circuit in which a second input/output port is alternately switched and used as an output terminal and an input terminal for a key scan signal.