Date   : Wed, 03 May 2006 21:31:10 +0100
From   : Sprow <info@...>
Subject: Re: Western Design Center W65C02S

In article <4458F3EB.9090406@...>,
   Peter Rendle <pete@...> wrote:
> I have read that it is possible to upgrade a standard model B using a 
> CMOS 65C02 here (http://www.sprow.co.uk/bbc/howto.htm#cmosupgrade)
>
> Does anyone know if the same applies to the WDC part?

I don't think so, or at least not directly.

The WDC parts have a few extra pins (variously previously N/C, same name but
opposite direction), the result is you'd need to do some track cuts and add
pullups as appropriate - for example one of the output pins is hardwired to
+5V on the BBC motherboard.

> Or would I be best building one into a second processor and running it 
> at 14Mhz? ( Probably tricky!!)

The intimate relationships between timing on the BBC means you can't easily
jack up the CPU rate without melting the VIAs/patching software timing loops
in filing systems/getting video coming out at the wrong rate/etc...

I'd suggest using one in a second processor would be simpler since you only
have the RAM timing to worry about then, and frankly there's no reason to
use DRAM for 32k now - a 70ns SRAM will suffice.

Of course I'd have to sway you towards an ARM coprocessor in favour of
trying to squeeze a WDC part onto the Tube,
Sprow.