cpdr.rst

CPDR

CPDR

Compare and Decrement with Repeat

Description

Performs cpd until either A = (HL) or BC = 0.

cp a,(hl)
dec hl
dec bc
jr nz,-7
ret po
jr -10

Uses

• Finding a certain letter in a string (or other similar tasks)

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)
cpir	$ED, $B1	2F + (Iterations)*(1R + 2) - 1 where Iterations is the number of iterations of cpd before either A = (HL) or BC = 0	3F + (Iterations)*(1R + 2) - 1	3F + (Iterations)*(1R + 2) - 1

Notes

• Interrupts can be triggered while this instruction is in progress (unless they are disabled using DI, of course).

See Also

CP, CPD, CPI, CPIR, LDDR