Tuesday, September 15, 2009

Interfacing of eight 7-segment digits

Statement: Interface 8/7-segment digits (common cathode) to 8085 through 8279 and write an 8085 assembly language program to display 1 to 8 on the eight seven segment digits. External clock frequency is 3 MHz.


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

Source program:
LXI B, 6200B : Initialize lookup table pointer
MVI C, 08H : Initialize counter
MVI A, 00H : Initialize keyboard/display
OUT 8IH : Mode
MVI A, 3EH : Initialize prescaler count
MVI A, 90H : Initial size 8279 in write Display
OUT 8IH : 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

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