Jos, You have sparked a funny (now) memory from my long distant past. In my youth, I had a Rockwell 65F11 SBC board, with a FDC, that was a small scale Forth development system. I spent many many hours writing code on it. One day, I decided that it needed a memory upgrade, and I designed a card to sit on top of the entire PCB that had buckets of ram (48K from memory??). As a trainee, I thought that I would be clever, an instead of laying out all of that tedious memory decode logic, I would use a 2732, and simply write a big decode matrix. (It worked beautifully for a traffic light controller state machine I did a little earlier...) So, I created an awesome memory upgrade PCB (with tape on film - 2 sided) - Photo reduce - expose - etch - drill - populate, etc, etc......All to discover that it didn't work.. After hours of trying to find the problem, I sheepishly approached one of the Senior Technical Officers, who suggested with a smile, that I connect a logic analyser to see what was happening... Low and behold - the CS* signal never got around to appearing before the memory was read. That day, I truly found out what 450nS access time actually meant. All to try to avoid mucking around with those pesky single use proms... Interestingly enough, a year or so later, I fitted one of those massive 62256 to get all of the memory I needed. Wo hoo. I hope you find a solution. BTW, does anybody remember the wierd diode logic decode that the TRS-80 model 1 used.... I tried that once as well, and discovered that you couldn't use silicon, and that only germanium worked. -- Doug Jackson, I-RAP, MAIPM, MIEEE Principal Information Security Consultant EWA-AUSTRALIA PO Box 6308 O'Connor ACT 2602 Level 1, 214 Northbourne Ave, Braddon ACT 2612 Tel: +61 (0)2 6230 6833 Fax: +61 (0)2 6230 5833 Mob: +61 (0)414 986 878 http://www.ewa-australia.com ============================================ IMPORTANT: This email remains the property of Electronic Warfare Associates - Australia. If you have received this email in error, you are requested to contact doug.jackson at ewa-australia.com or Ph +61 2 62306833 and delete the email. This message is not to be copied or distributed to other parties without the express permission of the author. Any personal information in this email must be handled in accordance with the Privacy Act 1988 (Cth). ============================================