Write a counter program to count continuously from 0 to 99 in BCD with a delay of 750ms between each count. Display the count at an output port.
Answers
Answer:
The count at an output port is given by 17.5 microseconds
Explanation:
- The hexadecimal counter is set by loading a register with starting number and decrementing it till zero is reached and then again decrementing it to will produce -1, which is two’s complement of FFH. Hence, the register again reaches FFH.
- The 1ms time delay is set up by the procedure shown in the flowchart-
The register is loaded with an appropriate number such that the execution of the above loop produces a time delay of 1ms.
Program:
Address Label Mnemonics
2000H MVI B, FFH
2002H NEXT DCR B
2003H MVI C, COUNT
2005H DELAY DCR C
2006H JNZ DELAY
2009H MOV A, B
200AH OUTPORT#
200CH JMP NEXT
The C register is the time delay register which is loaded by a value COUNT to produce a time delay of 1ms.
To find the value of COUNT we do-
TD = TL + TO
where- TD = Time Delay
TL = Time delay inside loop
TO = Time delay outside the loop
The delay loop includes two instructions- DCR C (4 T-states) and JNZ (10 T-states)
So TL = 14*Clock period*COUNT
=> 14*(0.5*10-6)*COUNT
=> (7*10-6)*COUNT
Delay outside the loop includes-
DCR B : 4T
MVI C, COUNT : 7T
MOV A, B : 4T
OUTPORT : 10T
JMP : 10T
Total : 35T
TO= 35*Clock period => 17.5 microseconds
