Zilog Z80380 Manual de usuario descargar pdf (Pagina 82)

5-48

Z380

™

USER'S MANUAL

DC-8297-03

ZILOG

DJNZ

DECREMENT AND JUMP IF NON-ZERO

DJNZ dst dst = RA

Operation: B ← B-1

If (B <> 0) then begin

dst ← SIGN EXTEND dst

if (XM) then begin

PC(31-0) ← PC(31-0) + dst(31-0)

end

else begin

PC(15-0) ← PC(15-0) + dst(15-0)

end

The B register is decremented by one. If the result is non-zero, then the destination address

is calculated and then loaded into the Program Counter (PC). Control then passes to the

instruction whose address is pointed to by the PC. When the B register reaches zero, control

falls through to the instruction following DJNZ. This instruction provides a simple method of

loop control.

The destination address is calculated using Relative addressing. The displacement in the

instruction is added to the PC; the PC value used is the address of the instruction following

the DJNZ instruction.

These instructions employ either an 8-bit, 16-bit, or 24-bit signed, two’s complement

displacement from the PC to permit jumps within a range of -126 to +129 bytes, -32,765 to

+32,770 bytes, or -8,388,604 to +8,388,611 bytes from the location of this instruction.

Flags: S: Unaffected

Z: Unaffected

H: Unaffected

V: Unaffected

N: Unaffected

C: Unaffected

Addressing Execute

Mode Syntax Instruction Format Time Note

RA: DJNZ addr 00010000 —disp— note X

DJNZ addr 11011101 00010000 -d(low)- -d(high) note X

DJNZ addr 11111101 00010000 -d(low)- -d(mid)- -d(high) note X

Note: 3 if branch not taken, 4 if branch taken

1 2 ... 77 78 79 80 81 82 83 84 85 86 87 ... 267 268

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Zilog Z80380 Manual de usuario Pagina 82