[Coco] eprom programmer

[Chad H]

This may be a shot in the dark, but a while back I got a batch of SST 29EE20
EEPROM's They are 256k @ 32-pn, so I have I would have 4 pins hanging over
the edge of the 502 ROM socket.

Question is, is anyone familiar with 29EE20's? (used in some older PC
motherboards for BIOS)  http://www.ebay.com/itm/190491783701  (examples)
If so, any possibility of making use this in the 502 Controller?  The
thought of having up to 32 selectable ROM's on one chip is...::drool: :~

I am still looking for PIN diagram for these, but so far nothing.
- Chad

-----Original Message-----
From: coco-bounces at maltedmedia.com [mailto:coco-bounces at maltedmedia.com] On
Behalf Of Frank Pittel
Sent: Saturday, March 24, 2012 2:53 PM
To: CoCoList for Color Computer Enthusiasts
Subject: Re: [Coco] eprom programmer

I'm thinking the same thing!! :-) I just need to figure out which ROM
version I would want besides drivewire. I do have a scsi adaptor but to use
that with a floppy controller means I'd need an MPI and I've got a SuperIDE
with the a version of jdb-dos with scsi support. It's nice to have the
option though!

The Other Frank


On Sat, Mar 24, 2012 at 01:32:49PM -0500, Chad H wrote:
> Hmm...Sounds like a project..Maybe I could select between DECB & 
> HDBDOS
> (DriveWire) that way.
> 
> -----Original Message-----
> From: coco-bounces at maltedmedia.com 
> [mailto:coco-bounces at maltedmedia.com] On Behalf Of Darren A
> Sent: Saturday, March 24, 2012 12:40 PM
> To: CoCoList for Color Computer Enthusiasts
> Subject: Re: [Coco] eprom programmer
> 
> 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
> 
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