Date   : Wed, 15 Aug 2012 16:14:08 +0200
From   : rick@... (Rick Murray)
Subject: Programatically "reset" a Beeb?

Hi,

I'm walking across a field (exercise! ~2km/day) listening to nano.RIPE, so
this is just a thought that occurred to me.

...namely... the addressing range of the 6502 is 64K yet the Master has 
more. This would suggest to me that bringing up the machine is a little more
complex. You don't say which ROM set actually fails, but I'd be kinda surprised
to see a Beeb MOS ROM working in a Master...


Best wishes,

Rick.

Richard Gellman <splodge@...> wrote:

>  
>
>Hi, 
>
>I'm having trouble with a "reset" process. Hopefully someone
>here can point out the Bleeding Obvious(tm) to me. 
>
>I've build a board
>for my M128 with two ROM sets, the original M128 set and the Model B
>OS1.2/Basic2 ROMs. Switching between them is under software control.
>
>
>Obviously, one do not simply change ROMs. So my procedure is thus:
>
>
>Disable interrupts (SEI) 
>
>Store 0 at ROMSEL (fe30) and ACCCON (fe34)
>to enable B-like memory mapping. 
>
>Store the bit in the ROM set select
>register (1MHz bus) 
>
>JMP (&FFFC) 
>
>Except, it doesn't quite work. It
>changes ROM set sure enough, but the start sequence is interrupted and
>scrolls uncontrollably, sometimes with characters on screen. 
>
>I tried
>blanking the 32K RAM beforehand, setting it all to &FF, and use of
>*FX200,3 but none worked. I'm clearly missing a clue on how to reset the
>state of the machine so it can start properly. 
>
>Any suggestions as to
>what I'm missing? 
>
>Thanks 
>
>-- Richard 
>
>  
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