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 the 7 segment display.
HARDWARE FOR 4x4 MATRIX KEYBOARD & 4 DIGIT 7 SEGMENT DISPLAY INTERFACE
Fig. shows interfacing diagram. Here, 4 scan lines are sufficient to scan matrix keyboard and to select display digits. Hence decoded mode is used.
SOFTWARE FOR 4x4 MATRIX KEYBOARD & 4 DIGIT 7 SEGMENT DISPLAY INTERFACE
To display 1 to 8 numbers on the eight 7-segment digits we have to load 7-segment codes for 1 to 8 numbers in the corresponding display locations.
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.
Step 4: Find Write FIFO RAM command word.
| Source program: - MVI A, 00H : Initialize keyboard/display in encoded
- OUT 81H : scan keyboard 2 key lockout mode
- MVI A, 34H
- OUT 81H : Initialize pre-scalar 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
| Flowchart for Source Program and Interrupt Service Routine 
|
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