Connect the 4 & TImes; 4 matrix keyboard with the parallel port P1 of AT89S51, with P3.0-P3.3
As the input line, use P3.4-P3.7 as the output line; display the serial number "0-9" of the digital buttons on the digital tube, and display 0 on the other buttons.
Principle analysis: Each key of the 4X4 matrix keyboard has its row value and column value. When the row value of each key is low and the column value is high, the key is not pressed. When judging whether a button is pressed, first let this row pass low level, then scan each column to judge whether it is pressed (column value to pass the high level), if it is pressed, then the power of this column At this time, it will become low level; if this column is low level during scanning, it means that a button is pressed in this column, and the row value is determined every time before judging the column value, so that you can know in the end Which button was pressed.
Basic process: Set the first line low level-> scan each column (set to high level), determine whether it is 0-> determine whether there is a key press-> set the second line low level-> Scan the second column ... (so loop to the fourth row and start over from the first row)
Compilation environment: KEIL C51 V3
Simulation software: proteus 7.4
SCM type: AT89C52
Digital tube type: 7seg-mpx1-cc (cc-common negative digital tube)
Keyboard type: keyboard-samllcalc
The program on the microcontroller is as follows:
#include "reg52.h"
char code table [] = {0x3f, 0x06, 0x5b, 0x4f, 0x66,
0x6d, 0x7d, 0x07, 0x7f, 0x6f};
sbit row1 = P3 ^ 4;
sbit row2 = P3 ^ 5;
sbit row3 = P3 ^ 6;
sbit row4 = P3 ^ 7;
int temp;
int key;
// void delay500ms ();
void delay20ms ();
void main ()
{
P1 = table [0];
while (1)
{
P3 = 0xff;
row1 = 0;
temp = P3;
temp = temp & 0x0f;
if (temp! = 0x0f)
{
delay20ms ();
temp = P3;
temp = temp & 0x0f;
if (temp! = 0x0f)
{
switch (temp)
{
case 0x0e:
key = 7;
break;
case 0x0d:
key = 8;
break;
case 0x0b:
key = 9;
case 0x07:
key = 0;
}
P1 = table [key];
}
}
P3 = 0xff;
row2 = 0;
temp = P3;
temp = temp & 0x0f;
if (temp! = 0x0f)
{
delay20ms ();
temp = P3;
temp = temp & 0x0f;
if (temp! = 0x0f)
{
switch (temp)
{
case 0x0e:
key = 4;
break;
case 0x0d:
key = 5;
break;
case 0x0b:
key = 6;
break;
case 0x07:
key = 0;
}
P1 = table [key];
}
}
P3 = 0xff;
row3 = 0;
temp = P3;
temp = temp & 0x0f;
if (temp! = 0x0f)
{
delay20ms ();
temp = P3;
temp = temp & 0x0f;
if (temp! = 0x0f)
{
switch (temp)
{
case 0x0e:
key = 1;
break;
case 0x0d:
key = 2;
break;
case 0x0b:
key = 3;
break;
case 0x07:
key = 0;
break;
}
}
P1 = table [key];
}
P3 = 0xff;
row4 = 0;
temp = P3;
temp = temp & 0x0f;
if (temp! = 0x0f)
{
delay20ms ();
temp = P3;
temp = temp & 0x0f;
if (temp! = 0x0f)
{
switch (temp)
{
case 0x0e:
key = 0;
break;
case 0x0d:
key = 0;
break;
case 0x0b:
key = 0;
break;
case 0x07:
key = 0;
break;
}
}
P1 = table [key];
}
}
}
/ *
void delay500ms ()
{
int i, j, k;
for (i = 0; i 《10/2; i ++）
{
for (j = 0; j 《180; j ++）
{
for (k = 0; k "200; k ++)
{
}
}
}
} * /
void delay20ms ()
{
int i, j;
for (i = 0; i 《36; i ++）
{
for (j = 0; j 《200; j ++）
{
}
}
}
The core part of the circuit diagram is as follows:
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