Re: gEDA-user: M68K bus and transmission line ringing

[Bob Paddock <bob.paddock@xxxxxxxxx>]

On Friday 19 October 2007 07:25:19 am Michael Sokolov wrote:

> I know there are a few old-timers on this list (by that I mean hardware
> engineers of old school), and my question is directed to those.  Would
> anyone here happen to experience designing a system with the good old
> Motorola MC68302?  

Those were the days... :-)

> I've been told that when a sufficiently fast-switching signal is driven
> onto a sufficiently long net, one has to worry about this signal ringing
> due to transmission line effects. 

The Motorola classics:

AN1051: Transmission Line Effects in PCB Applications [.PDF 1.5M] 
AN1061: Reflecting on Transmission Line Effects [.PDF 58k]

are worth a read.  You can find them on my site
at http://www.designer-iii.com/ do a search for "LVDS".


> I hope someone can give me some insight, preferably backed by some
> actual experience with M68K designs.

Pay particular attention to the timing margin of the Write# line,
been so long since I did 68K I don't recall what it was called,
but I do remember the Write Pulse could be much shorter than
you really wanted it to be when you looked at the setup&hold
times of the devices on the bus.  

Take a look at the "DTACK Grounded" archives:

http://www.amigau.com/68K/dg/dg.htm


-- 
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