Date   : Fri, 02 Sep 1994 14:11:23 +0100 (BST)
From   : clr1@...
Subject: Re: UNDEFINED 6502 OPCODES

Hello again folks... back at St. Andrews having just sat another 
disasterous resit. Anyway, at least E-mailing is free here! Anyway, back 
to beebing...

> for the purposes of 6502 emulation, is it really necessary to 
> investigate these so-called undefined opcodes? i find it
> difficult to believe that commercial software would dare use these.
> of course, i'm quite ready to be proven wrong.

I've implemented undefined opcodes as just incrementing the PC and 
returning, altering nothing. I've got a breakpoint in my program just in 
case one is used, but I didn't know that they actually *did* anything!

What's the point in using them? Are they undocumented instructions? Just 
wondering.

+-------------------+-------------------------------------------------+
| /-- |_| /-- | (~  | "And the driving is like the driving of Jehu,   |
| \-- | | |   | _)  | the son of Nimshi, for he drives furiously."    |
+-------------------+-------------------- Second Book of Kings 9 v20 -+