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From: apm279l@vaxc.cc.monash.edu.au
Newsgroups: comp.sys.handhelds
Subject: Questions RE: saturn processor (esp 28, also 48)
Message-ID: <72330.274a4cb2@vaxc.cc.monash.edu.au>
Date: 20 Nov 90 22:45:22 GMT
Organization: Computer Centre, Monash University, Australia
Lines: 36

Hi, I am working on (and have almost finished) a saturn -> C converter which
should make it simple to debug saturn code. If it is of interest I'll place
it in the public domain (that's the sweetener!) Now: I have a few questions
re the Saturn processor (I could find out for myself by experiment, but to
save me some time as I'm very snowed under at the moment...)

(1) According to the now biblical processor notes (thanks Alonzo!)
    the branch instructions affect the carry. I need to know *how*
    it is affected. I *guess* that (for example) brgt.f a,c,label
    does a subtraction, but is it "a-c" or "c-a"?? what about
    breq, brge, brle, brlt etc. What about brz and brnz??

(2) What about neg.f X - how is carry alterred? It could either take
    a two's complement by inverting and THEN incrementing, or by
    decrementing, THEN inverting.

(3) gosub, gosubvl, gosubl also affect carry - is this because the processor
    takes PC.a+OFFSET.a ?

(4) How do the IN and OUT registers get used? (I know they are used somehow
    for I/O - but what happens, for example when you put something in OUT,
    how does IN receive input? and from where? - I though the keyboard was
    bufferred in memory (#F.... something)

(5) What's known about the BUS commands? (BUSCB, BUSCC, BUSCD - do these put
    the contents of B,C or D on the bus? if so, what field is put?)
    CON/UNCONFIG, MOVE.A ID,C, SREQ, RESET. - I have the brief descriptions
    of these from Alonzo's notes, but what are the chips in question? What
    are the ID's, what happens when you config/unconfig/reset the chip?

I know there is a lot here, and I may not implement all these command in my
first release (depending on complexity) - but I'd like to make the converter
as realistic as I can. I have not seen any details on this stuff in c.s.h
and I imagine there'd be quite a few users out there with the same questions.

Thanx in adv, Peter