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RE: [N8VEM-S100:1331] terminating the backplane...
Much has been written over the years on bus termination! I will not attempt
that here. Just to say the best I have seen/used on the S-100 bus is the
Godbaut "active termination" approach. On a 21 slot motherboard I can get to
10MHz bus master clock fairly reliably with CPU's that are capable. 12MH is
a 10 card cage.
If you are doing it by hand with two resistors/line, the fun runs out of it
fast! If you just want to see if you are on the right track you can just
terminate the critical CPU signals pSync, pSTVAL, pDBIN and pWR*. These are
the absolutely critical signals and of short duration. All others should
long since be settled before these strike. Next up would be the status
signals sMEMR, SOUT,SINP and sINTA.
If you don't see a significant improvement with these then I would suspect
other issues. Things like bus loading, open collector lines shared with
regular Totem Pole TTL gates, or gates on lines conflicts where the driver
is "fatigued"/burned out due to signal conflicts. On more complex systems
(master/multiple slaves), a common problem is EACH board is pulling up an
open collector line thereby dropping the total bus line pull-up to < 1K.
Should be one per bus.
Anyway happy soldering!
From: n8vem...@googlegroups.com [mailto:n8vem...@googlegroups.com] On
Behalf Of Douglas Goodall
Sent: Monday, January 28, 2013 5:42 PM
Subject: Re: [N8VEM-S100:1331] terminating the backplane...
Not a bad idea for an N8VEM board. We have quite a few S-100 people, and
terminated motherboards are harder to come by. Beyond that, those of us who
realize our busses are not terminated are sad. :-(
On Jan 28, 2013, at 2:47 PM, Andrew Lynch <LYN...@YAHOO.COM> wrote:
> Hi Douglas! Thanks! Yes, it would be easy to build a bus terminator
> an S-100 Regular Prototyping board. Basically just copy the circuit
> from the S-100 backplane onto a S-100 regular prototyping board. It
> is a fairly simple circuit and works wonders on a noisy bus.
> Thanks and have a nice day!
> Andrew Lynch
>> -----Original Message-----
>> From: n8vem...@googlegroups.com [mailto:n8vem-
>> s1...@googlegroups.com] On Behalf Of Douglas W Goodall
>> Sent: Monday, January 28, 2013 1:51 PM
>> To: n8vem...@googlegroups.com
>> Subject: [N8VEM-S100:1329] terminating the backplane...
>> Is it possible to use a prototyping card to terminate an otherwise
>> unterminated backplane?
>> How would one go about testing the backplane to see if termination
>> issues are present?
>> Douglas Goodall
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