CP

CP M,N

Compare

Description

Subtracts N from M (and updates the flags accordingly), but doesn’t modify either operand.

M - N

Uses

• Comparing two bytes

Results

Register/Flag	8-bit
S flag	Set if the result is negative; else reset
Z flag	Set if M = N
H flag	Set if borrow from bit 4; else reset
P/V flag	Set if overflow; else reset
N flag	Set
C flag	Set if borrow; else reset

Allowed Instructions

Instruction	Opcode	CC (ADL/non-ADL)	CC (.S)	CC (.L)
cp a,a	$BF	1F	X	X
cp a,b	$B8	1F	X	X
cp a,c	$B9	1F	X	X
cp a,d	$BA	1F	X	X
cp a,e	$BB	1F	X	X
cp a,h	$BC	1F	X	X
cp a,l	$BD	1F	X	X
cp a,ixh	$DD, $BC	2F	X	X
cp a,ixl	$DD, $BD	2F	X	X
cp a,iyh	$FD, $BC	2F	X	X
cp a,iyl	$FD, $BD	2F	X	X
cp a,(hl)	$BE	1F + 1R	2F + 1R	2F + 1R
cp a,(ix+n)	$DD, $BE, n	3F + 1R	4F + 1R	4F + 1R
cp a,(iy+n)	$FD, $BE, n	3F + 1R	4F + 1R	4F + 1R
cp a,n	$FE, n	2F	X	X

Notes

• When using CP with signed integers, the flags are set as follows:

  • Z means M = N
  • NZ means M ≠ N
  • C means M < N
  • NC means M ≥ N

See Also

SUB, SBC, CPI, CPIR, CPD, CPDR