Date   : Wed, 09 Jul 2008 07:29:08 +0100
From   : info@... (Sprow)
Subject: ROM type byte inconsitancies

In article <080709015502@...>,
   Jonathan Graham Harston <jgh@...> wrote:
> The 32016 client does:
> The 80186 client does:
> The 6502 Tube and CoPro clients do:
> The 65Tube emulator client does:
> The Z80 client v1.20 does:
> The Z80 client v2.00 does:

[stuff]

> > The Master MOS's OSByte ROM header checking does
> >   IF bit6 clear "This is not a language"
> >   AND 13 * 2
> >   IF nonzero "I cannot run this code"
> > so 13x2 (%11010) seems to be being used to deduce whether it can be run 
> > by
>  
> That's after the MOS has already rotated the ROM type left one bit
> to transfer the "service" bit into the carry, so it's still
> effectively checking with AND #&0D.

Ah yes, I'd looked at the ASLA bit 6 checking but it'd not sunk in that it
didn't get shifted back. 

> The only sideways ROMs I've encountered are BASIC, 6502 and Z80
> using 0, 2 and 8 so I've no examples to inform me.

I can offer
  http://www.sprow.co.uk/bbc/hardware/armcopro/alphabet.zip
though of course I follow my own documentation and use 13,
Sprow.