CPD

CPD

Compare and Decrement

Description

Performs cp a,(hl), then decrements HL and BC.

cp a,(hl)
dec hl
dec bc

Uses

• This instruction is not very useful on its own, as cp a,(hl) is both smaller and faster than a single CPD, but more often used is the repeating version of CPD: CPDR

Results

Register/Flag	16-bit (non-ADL)	24-bit (ADL)
S flag	Set if result is negative; else reset
Z flag	Set if A = (HL); else reset
H flag	Set if borrow from bit 4; else reset
P/V flag	Set if BC ≠ 0 after the operation; else reset
N flag	Set
C flag	Not affected

Allowed Instructions

Instruction	Opcode	CC (ADL/non-ADL)	CC (.S)	CC (.L)
cpd	$ED, $A9	2F + 1R	3F + 1R	3F + 1R

See Also

CP, CPDR, CPI, CPIR, LDD