2716 with 100 nS access time - Lessons learnt by a Trainee Technical Officer in the dim, distant past...

[Doug Jackson - pesonal email]

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
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http://www.ewa-australia.com


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