Re: [stella] Thrust v0.9

Subject: Re: [stella] Thrust v0.9
From: Eckhard Stolberg <Eckhard_Stolberg@xxxxxxxxxxxxxxxxxxxxx>
Date: Sat, 17 Jun 2000 14:19:43 +0200
>Yeah, me too.  Currently I'm using PCAE 2.2.
>Also, all letters in THRUST don't light up.   The 'U' and the final 'T' are

PCAE and the free version of Stella don't support illegal opcodes. Z26
is the only emulator that Thrust currently works with.

>Hmm... what's the deal with an illegal opcode (lax, was it?)?  Was this a
>misprint for TAX, or is it something PCAE can't deal with really well?
>What's it for?

The 650x processor series uses one byte for the instruction. That would
allow 256 different instruction, but only about 150 of them are defined
to do something usefull. Now the other 100 instruction bytes don't just
get ignored when the 650x finds them. Usually they execute parts of two
different legal instructions. Most of the time the results are not too
usefull, but some commands would actually make some sense. The command
labeled LAX for example loads a value into the acumulator and the x-register
at the same time using less cycles and less space than the normal two
instruction method.

Ciao, Eckhard Stolberg

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