Cent.Mbeck%OZ.AI.MIT.EDU@mit-xx.ARPA (Mark Becker) (06/18/86)
This CPU board has a >50 nsec. glitch on the phase 1 (pin 25)
line due to a race condition between IC-8D (a 7474) and IC-12A (a
74LS04) being caught by IC-5D (a 74LS02) and then amplified by IC-3A
(a 74LS367).
The fix is two-fold: (1) Replace IC-8D with a 74LS74. This will
narrow the glitch such that a... (2) small capacitor installed between
IC12 pin 2 and ground. I found, after some experimenting, that 150 pF
worked find - glitch now gone.
Two CPU boards here had this problem. The extra pulse out was
causing timing problems on another board in the frame which was using
phase 1 clock to generate internal timing.
I would appreciate hearing from other XOR S-100 owners - there
are some mistakes in the schematics I received from U.S. Micro Sales
and a couple of problems in the CP/M BIOS they shipped with early
systems.
Mark Becker
-------djl@ptsfb.UUCP (Dave Lampe) (06/24/86)
Cc:
Sorry for posting this, but my mailer couldn't handle your
address. <Cent.Mbeck%OZ.AI.MIT.EDU@mit-xx.ARPA>
I have the XOR / IOMega system from US Micro. Unfortunatly I bought mine
right before they went out of business. The only documentation I got was
two copies of the memory board documentation. I suppose I should be glad
I got all the hardware. I would be happy to pay you to Xerox (tm) anything
else you have.
Dave Lampe @ Pacific Bell
{dual,qantel,ihnp4,hoptoad}!ptsfa!ptsfb!djl
(415) 823-2408
To: Cent.Mbeck%OZ.AI.MIT.EDU@mit-xx.ARPA
Subject: Re: Hardware CAUTION: XOR S-100 CPU Board (Rev. B)
Newsgroups: net.micro.cpm
In-Reply-To: <1440@brl-smoke.ARPA>
Organization: Pacific * Bell, San Francisco
Cc:
Bcc:
I have the XOR / IOMega system from US Micro. Unfortunatly I bought mine
right before they went out of business. The only documentation I got was
two copies of the memory board documentation. I suppose I should be glad
I got all the hardware. I would be happy to pay you to Xerox (tm) anything
else you have.
Dave Lampe @ Pacific Bell
{dual,qantel,ihnp4,hoptoad}!ptsfa!ptsfb!djl
(415) 823-2408