Date   : Fri, 02 Sep 1994 14:59:23 BST
From   : dyates@...
Subject: Re: UNDEFINED 6502 OPCODES

Tim Morley (tim@...) wrote:
> [...] I seem to remember that there are
> things in there that do actually something other then just a NOP. I
> beleiev that there are patterns in the way that the instructions are
> layed out, and some of the undocumented instructions are the correct
> things for the place in the patern!
> 
> Tim

I agree wholeheartedly. James and I have been discussing this most
of the afternoon (since my last message here). He thinks I am talking
about the 65C12, but I'm pretty convinced that even the humble old
6502 (even if only in it's CMOS clothes) was guilty as charged.

As I said to him, I've read an article somewhere documenting all
of the 'undefined' codes, and warning that they didn't work on all
CPUs - only certain models, or certain batches or something like that.

D.

     1 man year - 730 people getting the job done by lunchtime...
 Danny Yates, BT CEC, pp 6/3, 151 Gower Street, London, WC1E 6BA, UK
 Email: Danny.Yates@...     Phone: +44 171 728 7697
    or: cs92dty@...           Fax:   +44 171 387 6743