RE: [N8VEM-S100:1333] terminating the backplane...

[Andrew Lynch <lyn...@yahoo.com>]

Hi John!  Thanks!

The S-100 backplane (8-slot) uses active termination circuitry.  It does work as you say.  I have an older model (6-slot) on my bench and it holds all the pins at about 2.7V until they are asserted high or low.  It works well and is much more power efficient than the passive or two-resistor method.

If some builder had to get one quick, I would just copy the circuit from the S-100 backplane to a prototyping board.  However Douglas does raise a good point and we should also have an active terminator board for non-N8VEM/S100computers.com systems.  For debugging if nothing else.  

The S-100 active terminator board would be fairly simple since the circuitry is already proven and just has to be moved to an S-100 board.  However, there are many irons in the fire at the moment!

Thanks and have a nice day!

Andrew Lynch

--- On Mon, 1/28/13, John Monahan <mon...@vitasoft.org> wrote:

> From: John Monahan <mon...@vitasoft.org>
> Subject: RE: [N8VEM-S100:1333] terminating the backplane...
> To: n8vem...@googlegroups.com
> Date: Monday, January 28, 2013, 11:11 PM
> 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!
> John
> 
> 
> 
> -----Original Message-----
> From: n8vem...@googlegroups.com
> [mailto:n8vem...@googlegroups.com]
> On
> Behalf Of Douglas Goodall
> Sent: Monday, January 28, 2013 5:42 PM
> To: n8vem...@googlegroups.com
> Subject: Re: [N8VEM-S100:1331] terminating the backplane...
> 
> Andrew,
> 
> 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. :-(
> 
> Douglas
> 
> 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
> using
> > 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...
> >> 
> >> Friends,
> >> 
> >> 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?
> >> 
> >> Thanks,
> >> 
> >> Douglas Goodall
> >> 
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> 
> ---
> Douglas Goodall, http://goodall.com
> 
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> 
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