JPH04262413A - Key scan circuit for microcomputer - Google Patents

Abstract

PURPOSE:To make it possible to use an A/D converter for another application. CONSTITUTION:To (n) output ports P0-Pn, input nodes N1-Nn of key matrix section 3 are connected via resistors R0-Rn of interface section 2, and interface node 2 is connected to the input terminal AD of A/D converter for a microcomputer.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a key scan circuit for a microcomputer, and more particularly to an analog key scan circuit using an A/D converter.

0002

2. Description of the Related Art A conventional analog key scan circuit, as shown in FIG.
n×m matrix switches SW00 to SWnm of the scan switch unit 3 are used via a power supply unit 4 having a pull-up resistor R0 for each terminal of ADn. At this time, resistors R0 to Rm are (R1+R2+R3+...Rx)
= (x・R0)/(m-x), and if x is a number between 0 and m, then when switch SW0x is pressed, A/
Voltage V0SW0 input to D converter input terminal AD0
x becomes (x/16)·VDD.

Therefore, each A/D converter input terminal A
By sequentially reading the voltages input to the terminals for D0 to ADn, it is possible to determine which key among the switches SW00 to SWnm has been pressed. However, in general, depending on the accuracy of the A/D converter and the accuracy of the resistor, etc.
In a bit A/D converter, it is practical to scan about six switches per terminal.

0004

[Problems to be Solved by the Invention] This conventional microcomputer key scan circuit can only use about six switches for one A/D converter terminal, so in order to scan many switches, it is necessary to There was a problem in that several /D converter terminals were required.

[0005]

[Means for Solving the Problems] A key scan circuit for a microcomputer according to the present invention applies resistor-divided voltages of each of a plurality of input nodes generated by pressing a matrix switch constituting a key matrix section to an A/ In a key scan circuit of a microcomputer that is detected by a D converter terminal, a divided voltage source voltage is supplied from each corresponding output port of the microcomputer to each of the input nodes of the key matrix section, and each of the input nodes is connected to a diode. It is configured by providing an interface section that connects to one A/D converter terminal via a terminal.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be explained with reference to the drawings. FIG. 1 is a block diagram of one embodiment of the present invention. The input node N1 of the conventional scan switch section 3 shown in FIG.
~Nn are connected, and the interface unit 2 connects the A/D converter input terminal A of the microcomputer 1 from the nodes N1 to Nn through the diodes D0 to Dn, respectively.
Connected to D.

Now, switch S corresponding to output port P0
When scanning W00 to SW0m, first output ports P1 to Pn other than output port P0 at "L" level, and only output port P0 outputs "H" level. At this time, switch S00 to S0m one of them
When the button is pressed, the voltage V0S at the intersection N1 of resistors R0 and R1
W0x is V0SW0x=(x/16)・(VDD-V1) when V1 is the on-voltage of the P-channel transistor.
becomes.

Therefore, the voltage VAD input to the A/D converter terminal AD is VAD=V0SW0x-0.6=
(x/16) (VDD=V1-0.6).

By reading this voltage with an A/D converter, it becomes possible to determine which switch among the switches S00 to S0m has been pressed. After completing the scan for output port P0, scan P1 to Pn in the same way to set all switches SW00 to SW00.
SWnm can be scanned. Note that the diodes D0 to Dn are used so that the voltage applied to the A/D converter terminal AD is not affected by "L" level outputs from other ports.

0010

[Effects of the Invention] As explained above, the present invention uses only one A/D converter terminal by obtaining power from the output port of the microcomputer to generate a partial voltage when each key is pressed. Since a large number of keys can be scanned with just one key, the A/D converter can be used for other purposes, and the number of keys used is no longer limited by the number of A/D converters.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of one embodiment of the present invention.

FIG. 2 is a block diagram of an example of a key scan circuit of a conventional microcomputer.

[Explanation of symbols]

1 Microcomputer 2 Interface part 3 Key matrix section 4 Power supply section

Claims (1)

[Claims] Claim 1: A key matrix of a microcomputer that detects, at an A/D converter terminal of the microcomputer, resistor-divided voltages of each of a plurality of input nodes generated by pressing a matrix switch constituting a key matrix section.
In the scan circuit, a divided voltage source voltage is supplied to each of the input nodes of the key matrix section from the corresponding output port of the microcomputer, and each of the input nodes is connected to one A/D converter terminal via a diode. A microcomputer key scan circuit characterized by having an interface section connected to the microcomputer.