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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.

HARDWARE FOR EIGHT SEVEN SEGMENT DIGITS INTERFACE

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.

76.a-Interfacing of eight 7-segment digitsSOFTWARE FOR 8 x 7 SEGMENT DIGITS 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.

76.b-Interfacing of eight 7-segment digits The three steps needed to write the software are:

Step 1: Find keyboard/display command word.

76.c-Interfacing of eight 7-segment digits

Step 2: Find program clock command word

76.d-Interfacing of eight 7-segment digits

Step 3: Find Read FIFO/sensor RAM command word.

76.e-Interfacing of eight 7-segment 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 pre-scalar count
  • OUT 8IH
  • 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

Flowchart

76.f-Interfacing of eight 7-segment digits

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