Statement: Interface 4 x 4 matrix keyboard and 4 digit 7-segment display and write an tssembly language program to read keycode of the pressed key and display same key on :he 7 segment display.
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 service routine
MVI A, 40H : Initialize 8279 in read FIFO RAM mode
OUT 81H
IN 80H : Get keycode
MVI H, 62H : Initialize memory pointer to point
MOV L, A : 7-Segment code
MVI A, 80H : Initialize 8279 in write display RAM mode
OUT 81H
MOV A, M : Get the 7 segment code
OUT 80H : Write 7-segment code in display RAM
EI : Enable interrupt
RET : Return to main program
Fig. shows interfacing diagram. Here, 4 scan lines are sufficient to scan matrix keyboard and to select display digits. Hence decoded mode is used.
HARDWARE FOR 4x4 MATRIX KEYBOARD & 4 DIGIT 7 SEGMENT DISPLAY INTERFACE
SOFTWARE FOR 4x4 MATRIX KEYBOARD & 4 DIGIT 7 SEGMENT DISPLAY 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 RAM command word.
Step 3: Find Write FIFO RAM command word.
Source Program and Interrupt Service Routine
