[sdiy] CPU for CR8000

[Steve Lenham]

----- Original Message ----- 
From: "Mike" <profpep at hotmail.com>

>> Looks like there are two CPUs in the CR8000, and that each was updated at
>> some point during production.
>
> There is a problem here if you're looking for a replacement. The 8048 was 
> a
> mask programmed device, which means you need the official part. Intel did 
> do
> an 8748, which was an EPROM version intended for prototyping, which became
> more popular than they expected because it was useful for small runs and
> one-offs. It has been possible, (though it's going to be hacker archive 
> time
> to find out how), to extract the data from an 8048, so if there were no
> spares, it might be possible to replace the 8048, with a suitably 
> programmed
> 8748, provided a working live machine can be found to transplant the
> firmware from. Finding a programmer that will do 8748's may be
> 'interesting', too.

The DIY-friendly Willem EPROM programmers (www.willem.org) handle reading 
and writing (where possible) of the 8048/8748 family via a special adaptor. 
I have already read Roland mask-programmed ROMs myself.

If you want to take this route, a word of advice - the Willem MCS-48 adaptor 
assumes you are using 87xx parts, which need +18V applied to enable data 
readout. The 80xx ROM parts only require +12V, so it is necessary to add a 
Zener in series with the EA pin circuitry (I made this jumper selectable). 
Not doing this risks frying that precious, irreplacable ROM...

HTH,

Steve L.