[Coco] eprom programmer

[Darren A]

On Sat, Mar 24, 2012 at 10:49 AM, Chad H wrote:
> Hmm...so let me see if my thinking is correct here...
>
> I currently have a 8K 2764 EPROM in my 502 Controller... If I replaced this
> with a 27128 16K chip I could combine 2 .ROM files, write them, but I would
> be stuck on either the low or high bank.
>
> Now Darren said the high address line was tied to Vcc on the controller.
> What if I removed that and ran the Vcc to a switch along with ground and
> used the switch to flip Vcc/Ground on the high address pin...  Would this
> achieve the bank switching effect?
>

Yes.  You would need to bend out pin 26 (A13) on the EPROM or perhaps
cut the trace on the board.  Then connect a switch to that pin which
toggles between Vcc/Gnd and you have a switchable, banked EPROM.

A more elaborate modification would be to do the same with pins 1 and
27, then you can use a 27512 EPROM with eight banks of 8K.

Or..connect pin 26 to the CPU address line A13 and only put switches
on pins 1 and 27, giving you four banks of 16K.

Darren