JPS63188217A - Key scanning circuit - Google Patents

Abstract

PURPOSE:To reduce the power consumption of a key scanning circuit by starting a key scanning job after a key input detecting means detects the input of either one of keys. CONSTITUTION:When a momentary switch 11 is pushed, the output of a key input amplifier 18 is changed to an L level from an H level. This level change is applied to a delay line 22 of a key input detecting circuit 20 as well as to an exclusive OR circuit 25. Then the output of the circuit 25 is set at an H level for the delay time of the line 22 based on the change of the output of the amplifier 18 to an L level from an H level. As a result, a set/reset type flip-flop 27 is set under a setting state (H level) and a counter 1 is started to scan the output of a decoder 2 successively to H levels from H levels. Then the push of the switch 11 is detected by checking that the amplifier 18 is set at an H level when the output of an output amplifier 4 is changed to an H level from an L level.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a key scanning circuit for detecting input of keys having a matrix structure.

[Conventional technology]

Conventionally, input detection for switches with a matrix structure (hereinafter referred to as keys) has been performed by activating only one output from the key source to determine which key is turned on, and by determining which key is being pressed (active) at that time. This was determined by key scanning, a method that sequentially examines each key source.

[Problem that the invention seeks to solve]

In the conventional key scanning circuit described above, key scanning must be performed constantly in order to detect the key force, and the larger the target key matrix, the greater the hardware and power consumption. There is a drawback.

The conventional key force detection described above detects the key source while constantly scanning it, but the present invention detects a change in the key source when there is a key force, starts scanning based on the detection signal, and thereby This is to determine which key was used to input the input.

[Means for solving problems]

The present invention provides a key scanning circuit that detects input to each of a plurality of keys in a matrix structure by key scanning, and a key input detection means for detecting an input to any of the keys; The key input detection means includes a start means for starting the key scanning after detecting an input of any of the keys.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a circuit diagram showing an embodiment of the present invention, in which 1 is a counter, 2 is a decoder, 3 to 5 are output amplifiers, 6 is a matrix key, 7 to 15 are momentary switches, 16
is a pull-up resistor, 17 to 19 are key human power amplifiers, 2
0 is the key human power detection circuit, 21 to 23 are delay lines, 24 to 2
6 is an exclusive OR circuit. 27 is a set/reset type flip-flop which receives a signal from the key force detection circuit 20 and causes the counter 1 etc. to start key scanning of the matrix key 6.

Next, the operation of this circuit will be explained. "First, if the momentary switches 7 to 15 of the matrix key 6 are not pressed, the outputs of the output amplifiers 3 to 5"
L It is at level 11 (low level). Well, the inputs of the key human power amplifiers 17 to 19 are pull-up resistors 16.
The exclusive OR circuits 24 to 26 of the key human power detection circuit 20 are at the “H” level (high level).
It is level 11. For this reason, the set/reset type flip-flop 27 is also in the reset state ("L level"), and its output stops the counter 1 and makes all the outputs of the decoder 2 "L" level.

Next, a case where any of the momentary switches 7 to 15 is pressed will be described. For example, if the momentary switch 11 is pressed, the key manual amplifier 18
The output changes from "H" level to "L" level.

This change is input to the delay line 22 of the key human power detection circuit 20 and the exclusive OR circuit 25, and the delay time of the delay line 22 is the same as the change in the output of the key human power amplifier 18 from "HI+ level" to "L" level. The output of exclusive OR 25 is ゛°H
” level.

As a result, the set/reset type flip-flop 27 is set (“H” level), the counter 1 is activated, the output of the decoder 2 is sequentially scanned from the “L” level to the “H” level, and the output amplifier 3 -5 outputs are set to "H11 level" in sequence. Output of output amplifier 4 becomes "L".
By checking that the key human powered amplifier 18 goes to the "H" level when it changes from the "H" level to the "H" level,
It can be detected that the momentary switch 11 is pressed.

Further, the reset signal in the figure is input at the time when sequence 2 is completed.

〔Effect of the invention〕

As described above, the present invention has the advantage that constant key scanning is not required by detecting the point in time when the key force changes, and therefore power consumption does not increase in proportion to the size of the key matrix.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of an embodiment of the present invention. 1... Counter, 2... Decoder, 3-5 output amplifier, 6... Matrix key, 7-15... Momentary switch, 16... Pull-up resistor, 17-1
9... Key human power amplifier, 20... Key human power detection circuit, 21-23... Delay line, 24-26... Exclusive OR circuit, 27... Set/reset type flip-flop.

Claims (1)

[Claims] In a key scanning circuit that detects the input of each of a plurality of keys forming a matrix structure by key scanning, a key input detection means detects an input of any of the keys, and the key input detection means detects input of any of said keys and then
A key scanning circuit comprising initiation means for initiating scanning.