Statement: Interface an 8 x 8 matrix keyboard to 8085 through 8279 in 2-key lockout mode and write an assembly language program to read keycode of the pressed key. The external clock frequency is 2MHz. Use I/O mapped I/O technique. (Dont use any Interrupts)
Source program:
MVI A, 00H : Initialize keyboard/display
OUT 81H : in encoded scan keyboard-2 keylockout mode
MVI A, 34H
OUT 81H : Initialize prescaler count
BACK: IN 81H : Read FIFO status word
ANI 07H : Mask bit B3 to B7
JZ BACK : If 0, key is not pressed wait for key press else read FIFO RAM
MVI A, 40H : Initialize 8279 in read
OUT 81H : FI FO RAM mode
IN 80H : Read FIFO RAM (keycode)
HLT : Stop program execution.
HARDWARE FOR 8 x 8 MATRIX KEYBOARD INTERFACE
SOFTWARE FOR 8 x 8 MATRIX KEYBOARD INTERFACE
The three steps needed to write the software are:
Step 1: Find keyboard/display command word.
Step 2: Find program clock command word
Step 3: Find Read FIFO/sensor RAM command word.
