How many times will the following loop executed what is the

How many times will the following loop executed? what is the total delay of this subroutine assuming a standard 8051 processor at 11.0592 MHZ?(machine cycles, MOV-1, DJNZ-2, RET-2) DELAY: MOV R5, #100 BACK: MOV R2, #200 AGAIN: MOV R3, #250 HERE: DJNZ R3, HERE DJNZ R2, AGAIN DJNZ R5, BACK RET

Solution

HERE: DJNZ R2,HERE ; decrements R2 by 1 and if R2 is non zero goes to here, like wise loop runs for 200 times

DJNZ R5,BACK ; decrements R5 by 1 and if R5 is non zero goes to BACK, like wise this loop runs for 100 times, for each loop R2 initializes with 200 and iterates 200 times, so total iterations would be 200*100

Machine cycles:

DELAY: MOV R5,#100 ; 1 machine cycle

BACK: MOV R2,#200 ; 1 machine cycle

HERE: DJNZ R2,HERE; 2 machine cycles (200*2)

DJNZ R5,BACK ; 2 machine cycles

RET ; 2 machine cycles

total = 1(DELAY: MOV R5,#100)+1(BACK: MOV R2,#200)+((200*2)(HERE: DJNZ R2,HERE;)+1*2(DJNZ R5,BACK)+1(BACK: MOV R2,#200))*100(times)+2(RET)

total = 1+1+(400+2+1)*100+2

=40304 machine cycles

total delay is 40304*(12/11059000) = 0.0437 sec