Eprom question

[+Larry]

I have an excess of 27256-type eproms, and a shortage of 2764's. Does anyone know if I can use a 27256 in place of a 2764 or as a 27128? Looking at the pinouts, the difference that jumps out at me is that A13 and A14 are of course absent on the 2764, and pin 26 is N/C while 27 is the PGM pin on the 2764. So if I program the lower 8KB of the 27256, then insert it into an 8K cart, it looks like it should work properly. (?) Has anyone done this? -Larry

[jaybird3rd]

Yes, it should work. I'm using a 27256 in my 7800 console that contains both the stock BIOS and the DevOS BIOS (a total of 8K). I typically concatenate multiple copies of the binaries together to fill up the entire EPROM (four copies of 8K binaries or two copies of 16K binaries for a 27256, for example), just to be safe, and then I hardwire the extra address lines to GND when I install the EPROM so it always uses the lowest bank. It's been a while since I've done it, but I don't remember having to move any other pins.

[Urchlay]

So if I program the lower 8KB of the 27256, then insert it into an 8K cart, it looks like it should work properly. (?) Has anyone done this? -Larry

 

I've done something similar on the Atari 2600: burned a 4K ROM to a 27256, used with an old Pac-Man cart board with an inverter and a 24-pin socket... and a 28-pin socket plugged into the 24-pin socket, with some of the pins bent up... wrote it up here:

 

http://www.hardcoders.org/stelladoc/27256cart.txt

 

Don't think you'd need the inverter on an Atari8 cart though.

 

You could also burn 4 8K ROMs on your 27256 (concatenate them together), use DIP switches for the top 2 address lines, and have a 4-game multicart.

[joeventura]

You can get 2732s on Ebay for about $1 USD each

and 2764s for about $1.40 each

[jaybird3rd]

You can get 2732s on Ebay for about $1 USD each

and 2764s for about $1.40 each

Yeah, but ... what fun is that?

 

[tjlazer]

Yeah if you quad double a 256 it should work right?

[dinosaur]

Hi Larry!

 

You might want to look at this:

 

http://www.atariage.com/forums/index.php?showtopic=94730