The 8051 Instruction Set
Atmel 8051 Microcontrollers Hardware Manual 1-42
4316B–8051–02/04
1.14.23 JNC rel
1.14.24 JNZ rel
Function: Jump if Carry not set
Description: If the carry flag is a 0, JNC branches to the address indicated; otherwise, it proceeds with the next instruction.
The branch destination is computed by adding the signal relative-displacement in the second instruction byte to
the PC, after incrementing the PC twice to point to the next instruction. The carry flag is not modified.
Example: The carry flag is set. The following instruction sequence,
JNC LABEL1
CPL C
JNC LABEL2
clears the carry and causes program execution to continue at the instruction identified by the label LABEL2.
Bytes: 2
Cycles: 2
Encoding: 01010000 rel. address
Operation: JNC
(PC) ← (PC) + 2
IF (C) = 0
THEN (PC) ← (PC) + rel
Function: Jump if Accumulator Not Zero
Description: If any bit of the Accumulator is a one, JNZ branches to the indicated address; otherwise, it proceeds with the
next instruction. The branch destination is computed by adding the signed relative-displacement in the second
instruction byte to the PC, after incrementing the PC twice. The Accumulator is not modified. No flags are
affected.
Example: The Accumulator originally holds 00H. The following instruction sequence,
JNZ LABEL1
INC A
JNZ LABEL2
sets the Accumulator to 01H and continues at label LABEL2.
Bytes: 2
Cycles: 2
Encoding: 01110000 rel. address
Operation: JNZ
(PC) ← (PC) + 2
IF (A) ≠ 0
THEN (PC) ← (PC) + rel
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