Try doing a model in Protel using the signal integrity function.

Don't try the whole bus, just one circuit, get the IO technology, lengths,
widths, shape and board
layup and material correct and you'll get a reasonably close simulation - or
at least I did.

Assuming you're not going to let more than once device talk at once, you'll
need to do at least three simulations, one for each driver.

Try playing with the termination inspector and see what happens.  Also
fiddle with the pin capacitance of each device and see what the best and
worst
case in the data gives you.

The simulation predicted what we could see in real life with a scope and
spectrum
analyser (I was investigating an EMC emissions problem).

j.



-----Original Message-----
From: Bevan Weiss [mailto:[EMAIL PROTECTED]]
Sent: 27 September 2002 09:52
To: Protel EDA Forum
Subject: Re: [PEDA] OT: termination for a multidrop bidirectional bus


Unfortuneately not.  I've got the trial version of HyperLynx here, but it
doesn't allow the simulation of custom made setups.  I've had a couple of
setups simulated by a contact in the industry that has access to the full
version, this is what put me onto needing the termination.  However, it
isn't all that useful in a bidirectional design.  Or at least I wasn't too
sure how to use it in such a manner.

Thanks I'll check out that site.

----- Original Message -----
From: "John Haddy" <[EMAIL PROTECTED]>
To: "Protel EDA Forum" <[EMAIL PROTECTED]>
Sent: Friday, September 27, 2002 6:48 PM
Subject: Re: [PEDA] OT: termination for a multidrop bidirectional bus


> Bevan,
>
> I'd check out Howard Johnson's site at www.sigcon.com and look at his
> archives of topics. There are interesting notes such as:
>
> When to use AC Coupling
> Three Drop Bus
> Hairball Nets
> Both-ends Termination
> Bus Architecture and Timing
> AC Terminators
> Bidirectional Terminations
> ...etc.
>
> Dr Johnson's archive should be able to provide most of the answers you're
> looking for. I assume that you don't have access to HyperLynx or similar
> simulation tools?
>
> John Haddy
>
>
>
> > -----Original Message-----
> > From: Bevan Weiss [mailto:[EMAIL PROTECTED]]
> > Sent: Friday, 27 September 2002 4:07 PM
> > To: Protel EDA Forum
> > Subject: Re: [PEDA] OT: termination for a multidrop bidirectional bus
> >
> >
> > The speeds are ~30MHz, the length of the bus is hopefully to be less
than
> > 12"
> >
> > The goals are speed, size and cost (high speed, small size, low cost).
> > However the speed is pretty much set (30MHz) and the cost is the next
> > biggest concern.
> > The brands of bus devices used are:
> > Epson (S1D13506 LCD controller)
> > Motorola MCF5307 microprocessor
> > Micron SDRAM
> > Fujitsu FLASH memory
> > SMSC Ethernet Controller
> > Analog Devices AS21065L
> > none of these have inbuilt termination resistors, or any form of drive
> > control that I know of (please advise me if I'm wrong on this).
> >
> > The 32bits is pretty much required to maintain bus throughput.  A
> > serial bus
> > isn't an option.
> >
> > I'm leaning towards the AC termination method, as that consumes the
lowest
> > power.  However I'm not too sure whether the rise/fall times
> > would be quick
> > enough using such a termination method.  Any words of wisdom etc would
be
> > greatly appreciated, I can't seem to get much info from my
> > tutors, it would
> > seem it's slightly above most of them :(
> >
> > Thanks guys,
> > Bevan Weiss
> >
> >
> > ----- Original Message -----
> > From: "Tony Karavidas" <[EMAIL PROTECTED]>
> > To: "'Protel EDA Forum'" <[EMAIL PROTECTED]>
> > Sent: Friday, September 27, 2002 5:28 PM
> > Subject: Re: [PEDA] OT: termination for a multidrop bidirectional bus
> >
> >
> > > What sort of speed are you running? What length is this bus. What are
> > > you goals for the project: speed, size, cost?? Do you need 32 bits?
> > > Could you incorporate a serial bus? What brand do you intent to use?
> > > Some have series resistors built in (Phillips). Depending on your
> > > answers, you could go from no termination to any method you mentioned
> > > below. Welcome to the world of engineering and design tradeoffs...
> > >
> > >
> > >
> > > > -----Original Message-----
> > > > From: Bevan Weiss [mailto:[EMAIL PROTECTED]]
> > > > Sent: Thursday, September 26, 2002 9:53 PM
> > > > To: Protel EDA Forum
> > > > Subject: Re: [PEDA] OT: termination for a multidrop bidirectional
bus
> > > >
> > > >
> > > > Hi,
> > > > sorry to ask this question to you guys, but I'm more likely
> > > > to get an answer from the people dealing with the technology
> > > > so to speak...
> > > >
> > > > What kind of termination is applicable for a multidrop
> > > > bidirectional bus (using LVTTL signals)??  I've thought about
> > > > series termination, one for each driver on the bus (however
> > > > that would total 256 resistors for a 32bit wide bus).  Thus
> > > > it's not my preferred method.  I also would prefer to avoid
> > > > parallel termination (or thevenin equilavent or ac
> > > > termination for that
> > > > matter) just because they would take up more inter-trace spacing.
> > > >
> > > > I'm sure that many of you have had this kind of situation
> > > > before and have some advice.  It's for a student design
> > > > project and the deadline is quickly approaching.
> > > >
> > > > Thanks,
> > > > Bevan Weiss
> > > >
> > >
> >
>

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