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The 8051 Instruction Set

1-41 Atmel 8051 Microcontrollers Hardware Manual

4316E–8051–01/07

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: 0 1 0 1 0 0 0 0 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: 0 1 1 1 0 0 0 0 rel. address

Operation: JNZ

(PC) ← (PC) + 2

IF (A) ≠ 0

THEN (PC) ← (PC) + rel

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Atmel C51 Handbuch Seite 43