[A83] Re: ex af,af'

[A83] Re: ex af,af'

• To: assembly-83@lists.ticalc.org
• Subject: [A83] Re: ex af,af'
• From: Patai Gergely <patai.ti@freemail.hu>
• Date: Sun, 30 Dec 2001 18:24:21 +0100 (CET)
• In-Reply-To: <000701c190ea$441728c0$041a450a@campus.mdh.se>
• Reply-To: assembly-83@lists.ticalc.org

> What is the difference between
> 
>    push af
>    ld a,d
>    lcddata
>    pop af
> 
> and:
> 
>    ex af,af'
>    ld a,d
>    lcddata
>    ex af,af'
> 
If the lcddata part depends on the initial value of the 
flags register and/or it uses the ex af,af' instruction 
somewhere, the routine is likely to give wrong results. You 
have to keep in mind that the stack is a (normally) safe 
place, but the shadow registers aren't. The most important 
difference is that when you're "saving" af, both a and f 
will be altered if you use "ex af,af'", as opposed to
"push af", which changes only sp and (sp), but preserves 
the old values of a and f.

PG

• [A83] Re: ex af,af'
• From: =?ISO-8859-2?Q?Jens_Bj=F6rnhager?= <jensbj@home.se>

• [A83] ex af,af'
• From: =?iso-8859-1?Q?Jens_Bj=F6rnhager?= <jensbj@home.se>

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