Path: utzoo!attcan!uunet!lll-winken!ames!ucsd!rutgers!att!petsd!fredc
From: fredc@petsd.UUCP (Fred Cassirer)
Newsgroups: comp.sys.amiga
Subject: Memory boards and bus noise
Message-ID: <1430@petsd.UUCP>
Date: 24 Jan 89 03:46:22 GMT
Organization: Concurrent Computer Corporation
Lines: 49


 I am involved in building a memory board (well I wrote some memory tests
 and other S/W stuff ...) for an Amiga 1000, and we are having a problem
 with what we think is bus noise.

 The board checks out ok, we can read/write and read-modify-write all fine
 by reading/writing before doing an ADDMEM (we have disabled the autoconfig
 stuff).  We can successfully "poke" an assembly program into the memory and
 the execute it via an indirect function call in C.  All seems well.

 We can ADDMEM, but soon afterwards (like after run emacs) we will guru.  Usually
 during a disk I/O (but I can't prove that).  Most of the time it looks like
 something has written all thru chip memory because the screen goes nuts.

 On the analyzer we are seeing noise glitches on the control signals (AS, R/W).
 We have heard that some kind of bus termination may clean up the problem.

 Does anyone know what buses or signals should be terminated and what to use
 for termination?

 We have new pals (10ns) and have done the grounding trick.
 I'm told the board is very "clean" as far as signals go, the
 memory chips are very fast (in the 25ns range)

 Following is a rough sketch of what we see happening:

 AS -------.                                           /\._______
           |  /\______________________/\/\____________|
            \/
 Data                                 .---------.
  Bus ________________________________|         |__________
                                      |_________|

  RW  ________________________________/\  __________________
         |                               \/         |
         `- - - - - - - - - - - - - -.  /\.- - - - -'
                                      \/
  GRND _______________________________  /\___________________
                                      \/

   Sorry if my graphics are a bit poor.

  Any help would be greatly appreciated.
					Thanx.
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<  Fred Cassirer			   ... rutgers!petsd!fredc or	   >
<  Concurrent Computer Corp	(preferred)... rutgers!petsd!pecnos!fredc  >
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