Re: A83: Opcode questions...

To: assembly-83@lists.ticalc.org
Subject: Re: A83: Opcode questions...
From: Scott Dial <homosapian@geocities.com>
Date: Sun, 30 May 1999 15:01:47 -0500
Delivered-To: assembly-83-outgoing@towerguard.unix.edu.sollentuna.se
Delivered-To: assembly-83@lists.ticalc.org
Organization: ByMe Inc. Technologies
References: <27a77673.2482dbf7@aol.com>
Reply-To: assembly-83@lists.ticalc.org


ld b,b and all of those are there because when you design a logical
system, such as a microchip, rather than have undefined states you
simply make it whatever is easiest. So instead having to make exceptions
for every register (ie. skip the ld self,self) they include it.

Ted21@aol.com wrote:
> 
> I am working on a z80 discompiler right now so that I can view the 1.07 ROM
> in all of its glory, but I've noticed some wierd things with the z80
> instructions.  I am basing my discompiler off of a text file called "opcodes"
> which is circulating around the internet somewhere and there are two specific
> questions I have.  First, for each register there is a command "ld b,b" and I
> am wondering what the purpose of something like this is because I think it is
> something like the equivalent of X->X in Basic.  Second, I have seen a couple
> of things like "jr nz,$+2" and am not entirely sure what this means.  Does it
> mean to jump two bytes ahead of the current address?  Any help you guys could
> give would be appreciated.
> 
> Ted21@aol.com

-- 
Scott "_Wrath_" Dial
homosapian@geocities.com
ICQ#3608935
http://www.geocities.com/~homosapian/

References:

A83: Opcode questions...

From: Ted21@aol.com