Keyboard-interface(64-key-matrix-keyboard)-Program71- Free 8085 Microprocessor projects

Source program

MVI A, 90H : Initialize Port A as input and

OUT CR : Port B as Output

START: MVI A, 00 : Make all scan lines zero

OUT PB

BACK: IN PA

CPI FF : Check for key release

JNZ BACK : If not, wait for key release

CALL DELAY : Wait for key debounce

BACK 1: IN PA

CPI FF : Check for key press

JZ BACK 1 : If not, wait for key press

CALL DELAY : Wait for key debounce

MVI L, 00H : Initialize key counter

MVI C, 08H

MVI B, FEH : Make one column low

NEXTCOL: MOV A, B

OUT PB

MVI D, 08H : Initialize row counter

IN PA : Read return line status

NEXTROW: RRC : Check for one row

JNC DISPLAY : If zero, goto display else continue

INR L : Increment key counter

DCR D : Decrement row counter

JNZ NEXTROW : Check for next row

MOV A, B

RLC : Select the next column

MOV B, A

DCR C : Decrement column count

JNZ NEXTCOL : Check for last column if not repeat

JMP START : Go to start

Fig. shows a matrix keyboard with 64 keys connected to the 8085 microprocessor using 8255. A matrix keyboard reduces the number of connections, thus the number of interfacing lines. In this example, the keyboard with 64 keys, is arranged in 8 x 8 (8 rows and 8 columns) matrix. This requires sixteen lines from the microprocessor to make all the connections instead of 64 lines if the keys are connected individually. The interfacing of matrix keyboard requires two ports: one input port and other output port. Rows are connected to the input port, port A and columns are connected to the output port, port B.