1. Conditional Jumps and Time Delays
Source:

4. Source: http://www.keil.com/support/man/docs/is51/is51_nop.htm

5. A single-loop time delay
“DJNZ” can be used here.

6. The DJNZ Instruction
DJNZ byte, rel decrement and jump if not zero (PC) <- (PC) + instructionSize (byte) <- (byte) - 1 IF (byte) <> 0 THEN (PC) <- (PC) + rel
2-byte version, used with Rn, n = 0 7
3-byter version, used with RAM location
DJNZ Rn, rel decrement and jump if not zero (PC) <- (PC) + 2 (Rn) <- (Rn) - 1 IF (Rn) <> 0 THEN (PC) <- (PC) + rel
DJNZ direct, rel decrement and jump if not zero (PC) <- (PC) + 3 (direct) <- (direct) - 1 IF (direct) <> 0 THEN (PC) <- (PC) + rel
11011rrr rel
bit add, rel
DJNZ R5,rel
DJNZ 30H, rel
rel
rel

7. MOV
MOV R0, 0FFH DJNZ R0, $

8. A 2-loop time delay
The overall number of iterations
= N0 × N1

9. A 3-loop time delay

10. A 3-loop time delay ; *** The 3-loop time delay *** threeLoopDelay:
MOV R2, #0AH
loop: CALL twoLoopDelay
twoLoopDelay:
; **** The 2-loop time delay ****
MOV R0, #0FFH
loadR1:
MOV R1, #0FFH DJNZ R1, $ DJNZ R0, loadR1 RET

11. JC & JNC
JC rel jump if carry set (PC) <- (PC) + 2 IF (C) = 1 THEN (PC)< - (PC) + rel
JNC rel jump if carry not set (PC) <- (PC) + 2 IF (C) = 0 THEN (PC) <- (PC) + rel

12. JZ & JNZ
JZ rel jump if accumulator zero (PC) <- (PC) + 2 IF (A) = 0 THEN (PC) <- (PC) + rel
JNZ rel jump if accumulator not zero (PC) <- (PC) + 2 IF (A) <> 0 THEN (PC) <- (PC) + rel

13. JB, JBC, & JNB JB JBC JNB PC = PC + 3 IF (bit) = 1 PC = PC + offset
JB P1.2 LABEL
JBC P1.2 LABEL
JNB P1.3, LABEL