Statement: Interface an 8 x 4 matrix keyboard to 8085 through 8279.
Source program:
MVI A, 00H : Initialize keyboard/display in encoded
OUT 81H : scan keyboard 2 key lockout mode
MVI A, 34H
OUT 81H : Initialize prescaler count
MVI A, 0BH : Load mask pattern to enable RST 7.5
SIM : mask other interrupts
EI : Enable Interrupt
HERE: JMP HERE : Wait for the interrupt
Interrupt Subroutine:
MVI A, 40H : Initialize 8279 in read FIFO
OUT 81H : RAM mode
IN 80H : Read FIFO RAM (keycode)
EI : Enable Interrupt
RET : Return to main program
HARDWARE FOR INTERFACING 8x4 MATRIX KEYBOARD
SOFTWARE FOR INTERFACING 8x4 MATRIX KEYBOARD
Fig. Interfacing 8 x 4 keyboard matrix in decoded scan keyboard mode.
NOTE: As keyboard is having 8 rows and 4 columns, only 4 scan lines are required and we can avoid external decoder to generate scan lines by selecting decoded scan keyboard mode.
