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Generate and display the contents of decimal counter

Published on Nov 18 2009 // Working with Counters

Statement: Write assembly language program to with proper comments for the following: To display decimal decrementing counter (99 to 00) at port 05 H with delay of half seconds between .each count. Write as well the delay routine giving delay of half seconds. Operating frequency of microprocessor is 3.072 MHz. Neglect delay for the main program.

Source Program: 

  • MVI C, 99H : Initialize counter
  • BACK: MOV A, C
  • ANI OF : Mask higher nibble
  • CPI OF
  • MOV A, C
  • SUI 06 : Subtract 6 to adjust decimal count
  • MOV D, A
  • SKIP: MOV A, C
  • OUT 05 : send count on output port
  • CALL Delay : Wait for 0.5 seconds
  • DCR C : decrement count
  • MOV A, C
  • CPI FF
  • JNZ BACK : If not zero, repeat
  • HLT : Stop execution

Delay subroutine:

  • Delay: LXI D, Count
  • Back: DCX D : 6 T-states
  • MOV A, D : 4 T-states
  • ORA E : 4 T-states
  • JNZ Back : 10 T-states
  • RET

52.Generate and display the contents of decimal counter 

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