[Coco] [Color Computer] Re: Coco flash cartridge

[Mark McDougall]

James Diffendaffer wrote:

> That's ok for a prototype but for production you have to remember that
> most people would want to reuse a game cart case if it will fit.  That
> probably means some sort of right angle switch or solder pads to
> attach a remote switch.  And if you plug it into a multipak interface
> you would have to feel around for the button even if the board isn't
> in a case if you use that button.

Yeah, this is really just a prototype, because if it went into production, 
the tooling costs would have to be re-done for a panel anyway. I only have 
one Coco cart atm - DoD - and I'm not about to rip _that_ apart! ;)

> I suppose you might be able to have a timer in your PLD
> as an alternative.

If there's enough register bits left for a long enough timer, then sure!

> LOL... don't you just hate scope creep?

And it's worst when you're spec'ing your own design! ;)

>>> I'd like to develop some stuff for the board, let me know how much >>it
>>> will cost for one. If you can provide the info on the ports ahead
>>> of time that would be nice.

I did my BOM at lunchtime today. Farnell want $15 for a 4MB flash. I haven't 
tried sourcing it anywhere else yet.. the other parts are almost 
negligible... the CPLD should cost a few dollars IIRC...

> Read only is fine... we'll just have to track the page in software. 

Unfortunately, D2 & D3 are wired to input-only pins on the CPLD. I 
originally had RESET# & CART# wired to them, and didn't realise until I had 
almost finished the layout. It was too difficult to wire any of the address 
lines to those pins, so D2&3 it was. I didn't think there'd be a real need 
to read the bank as it is not unusual to have shadow registers in software 
anyway. Alternatively I could always make it readable via the 2 high nibbles 
of address 0 & 1 if need be. In most cases it'll only be paging small ranges 
so it may only need the LS bits anyway....

> Sounds fine to me but I haven't programmed flash chips directly in
> years and back then you even needed to manually erase them.

These parts erase in 64KB pages - at least the 4MB one does. Programming is 
done by writing a 'magic sequence' to certain addresses and IIRC you can't 
read whilst erasing (I'd have to check) but you simply need to poll the 
RDY/BSY# bit until it's done.

> You have to be able to reset until artifact colors are correct without
> resetting the bank but you must be able to reset the bank without
> turning the machine off.  And since the system will probably die in a
> horrible manner if you reset the bank you are better off just
> resetting the system along with it.

Thanks for the feedback!
Regards,

-- 
|              Mark McDougall                | "Electrical Engineers do it
|  <http://members.iinet.net.au/~msmcdoug>   |   with less resistance!"