Statement: Write an assembly language program to roll message 'HELL0123' from right to left
Source program:
LXI B, 6200B : Initialize lookup table pointer
MVI C, 08H : Initialize counter
MVI A, 10H : Initialize keyboard/display in right entry mode
OUT 8IH : Mode
MVI A, 3EH : Initialize prescaler count
OUT 8IH
MVI A, D0H : Clear Display
OUT 8IH
MVI A, 90H : Initialize 8279 in write display
OUT 81H : RAM mode
BACK : MOV A, M : Get the 7-segment code
OUT 80H : Write 7-segment code in display RAM
INX H : Increment lookup table pointer
DCR C : Decrement counter
JNZ BACK : if count = 0 stop, otherwise go to back
HLT : Stop program execution
Fig. shows the interfacing of eight 7-segment digits to 8085 through 8279. As shown in the figure eight display lines (Bo-B3 and Ao-A3) are buffered with the help of transistor and used to drive display digits. These buffered lines are connected in parallel to all display digits. So, Sl and S2 lines are decoded and decoded lines are used for selection of one of the eight digits.
HARDWARE FOR ROLLING HELLO123
SOFTWARE FOR ROLLING HELLO123
To roll above message we have to load 7-segment codes for characters within the message and it is necessary to configure 8279 in right entry mode
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 display RAM command word.
