Date   : Tue, 30 Aug 1994 09:40:16 +0100
From   : jfid@... (James Fidell)
Subject: Re: BBC default boot mode.

Stephen Quan wrote:

> >From what I can understand, when the BBC powers on for the first time
> it gets the bootup mode from dip switches.  When you do a soft boot
> it checks (a register?) a bit of memory that tells it the boot mode
> which you can set using a *FX command.
> 
> Ok, I got this far, could someone tells me where the 6502 gets a clue
> of what mode you should be in???  When I got the emulator up, it seems
> to put the thing into mode 0.  I trapped the writes to the 6845 and I
> see it setting the 6845 registers to that required for MODE 0 operation.
> (Not exactly the same, some are out by 1).  Also, when I do a
> 
>   PRINT  ?&355
> 
> It reports 0, which could mean that either I don't have ?&355 working
> yet or I am indeed in mode 0.  How would I trick the thing into believing
> I am in mode 7 as soon as it boots up??

The DIP switches form part of the keyboard -- they act like keys that
are permanently open or closed and they're scanned at boot time to see
what mode to boot into etc.

I'd think it would be difficult to fake up something to enter MODE 7.

James.

-- 
 "Yield to temptation --             |
  it may not pass your way again"    |     jfid@...        
                                     |
        - Lazarus Long               |              James Fidell