[sdiy] Sanity Check please

[Tom Arnold]

On Mon, Feb 07, 2005 at 10:18:19PM +1100, Ken Stone wrote:
> possible better soltion -
> 
> use the first chip select line as the A13 address line. No inverter needed.

Actually there are 4 banks of ROMs.

The circuit is kinda cool in an 80's sorta way.  Bank of 4 mask programmed
ROMs ( all Mostek crap roms that die in 10 years of course ), an FPLA ( that
should give you a hint on age ) and a pair of 2k patch roms.  To bugfix the
main roms they originally sent out a new pair of patch eproms and a new FPLA.
The FPLA snags certain addresses and rewrites them to the patch roms.

Maybe this was common but I've never seen it before...

The rom images I've gotten were created by reading out the data from the
cards edge connector, so all the patches are included in the dump but also
the two banks of mask programmed roms are read into one larger bank which is
why I'm wedging in a pair of larger chips, but the patch roms still have to
be active for some reason no-one has bothered to look into.

If this becomes an addiction, I may OldCrow the rom board.  Make a nice new
one that fits the footprint but with a huge modern rom on it that covers
everything.  As it is I have to make ugly adapters because the Mostek pinout is
rather different then a standard 2764.

-- 
 ------------------------------------------------------------------------
 - Tom Arnold -       When I was small, I was in love,                  - 
 - Sysabend   -       In love with everything.                          -
 - CareTaker  -       And now there's only you...                       - 
 --------------         -- Thomas Dolby, "Cloudburst At Shingle Street" -