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DJNZ Instruction UM018809-0611

100

ZNEO

CPU Core

User Manual

DJNZ

Definition

Decrement and Jump if Non-Zero

Syntax

DJNZ dst, urel4

Operation

dst  dst

– 1

if dst

0 {

PC  PC + {FFFF_FFH, 111B, urel4, 0B}

}

Description

This instruction decrements the destination register and then performs a conditional jump if the

result is nonzero. Otherwise, the instruction following the DJNZ instruction is executed.

In assembly language, the jump destination is typically specified as a label or 32-bit address

operand. The ZNEO CPU assembler automatically calculates a relative offset and generates the

appropriate DJNZ opcode. The jump destination address is the PC value plus the calculated off-

set.

In object code, the offset operand is a 4-bit unsigned value corresponding to bits [4:1] of a nega-

tive PC offset. In practical terms, if urel4=0, the offset is –16 words. If urel4=FH, the offset is –1

word. The offset is measured from the instruction following DJNZ.

Flags

76543210

C Z S V B CIRQE IRQE

*****–––

Legend

C = Set to 1 if the result generated a borrow; otherwise set to 0.

Z = Set to 1 if the result is zero; otherwise, set to 0.

S = Set to 1 if the result msb is 1; otherwise set to 0.

V = Set to 1 if an arithmetic overflow occurs; otherwise set to 0.

B = Set to 1 if the initial destination value was 0; otherwise set to 0.

CIRQE = No change.

IRQE = No change.

1 2 ... 111 112 113 114 115 116 117 118 119 120 121 ... 215 216

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Zilog Z16F2810 Manual de usuario Pagina 116