PUSH / Discussion

This is the discussion related to the wiki page PUSH.

Wrong description

thirdflux 09 Apr 2013 14:23

hi there,
"Decreases SP by 2, then copies the operand into (SP)." is wrong for push reg16

it's more like "Copies operand to (SP), then increases SP by 2"

regards

Re: Wrong description

MattiWens 25 Mar 2024 13:55

This is wrong, the page needs editing.

"If you use push hl, first the value of SP is decremented by two, then virtually an ld (sp),hl happens".

error (guest) 03 Nov 2019 11:03

It is incorrect that PUSH "Copies the operand into (SP), then increments SP by 2."

From the Zilog Z80 manual:

Operation
(SP – 2) ← qqL, (SP – 1) ← qqH

Description
The contents of the register pair qq are pushed to the external memory last-in, first-out
(LIFO) stack. The Stack Pointer (SP) Register pair holds the 16-bit address of the current
top of the Stack. This instruction first decrements SP and loads the high-order byte of register
pair qq to the memory address specified by the SP. The SP is decremented again and
loads the low-order byte of qq to the memory location corresponding to this new address
in the SP. The operand qq identifies register pair BC, DE, HL, or AF, assembled as follows
in the object code: