2 Write a DELAY Subroutine that takes about 0004 seconds to

2. Write a DELAY Subroutine that takes about 0.004 seconds to execute. Include the algebraic expression for this delay routine, and show all calculations for how you determined your delay counter values. (a two-loop routine should be sufficient)

Solution

You havent mentioned for any processor name. So I am giving for 8085

Assume clock frequency = 3MHz

Clock period = 0.333us

Required T states = 0.004s/0.333us = 12012. The value of count is high so we take register pair BC

CODE :

LXI B , COUNT ; 10T lower address in B and higher address in C

LOOP DCX B ;6T

MOV A,B ; 4T move lower address in A

ORA C ;4T check if both A and C are zero

JNZ LOOP ;10/7T

RET ; 10T

Time delay = 10 + COUNT X (6+4+4+10) -3 + 10 = 12012

24COUNT = 12012 - 17 = 11995

COUNT = 500 dec = 01F4 H

NOTE : -3 in counting Time delay is because when JNZ executes in loop it has 10T states but if it fails , it has 7T states , so we have to remove 10 and add 7 since it executed inside loop.