Djnz – Zilog Z16F2810 User Manual
Page 116
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
7
6
5
4
3
2
1
0
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.