On Mon, 28 Jan 2008, Alexis wrote: I see 1 is Vpp (which won't be used anyhow). The extra address pins are 26 and 27. Am I right? -- David Griffith dgriffi at cs.csubak.edu

Basically the extra two address lines come from: Pin 27 was PGM on 2764 is A14 on 27256 Pin 26 was N/C on 2764 is A13 on 27256 These pins are *supposed* to be tied to +5 on a 2764 socket. Pin 27 is tied high as per specs on the chip, and this is usually the case. Pin 26 is tied high for backward compatibility with 24 pin parts, and this is not always implemented, sometimes it's N/C, sometimes it's grounded. Check your board and if this is the case (pins 26 and 27 tied high) you can use a 27256 without any cuts/straps by programming your code into the TOP 8K of the device. If pin26 is grounded, you can put the code at the 3/4 boundary $6000) - Or you can do what I often do and simply program it 4 times at all 8k blocks. If you have to cut/strap, consider putting in jumpers or a DIP switch which lets you have 4 "virtual EPROMS" which you can select. Dave -- dave06a (at) Dave Dunfield dunfield (dot) Firmware development services & tools: www.dunfield.com com Collector of vintage computing equipment: http://www.classiccmp.org/dunfield/index.html

On Sun, 27 Jan 2008, UnR00ster wrote: Interesting. This makes me think it would be better to use those extra address lines to bank-switch alternate firmwares. -- David Griffith dgriffi at cs.csubak.edu