please see embedded remarks below.
Dick
-----Original Message-----
From: Allison J Parent <allisonp_at_world.std.com>
To: Discussion re-collecting of classic computers
<classiccmp_at_u.washington.edu>
Date: Tuesday, June 01, 1999 9:00 PM
Subject: Re: Re[4]: More Bringing up a CPM
><Even if you don't intend to use PROMs in your final device, I'd certainly
><recommend you build a few PROMS which make the processor do rudimentary
><things and perhaps which make the DMAC do the same things. You then have
><simple tools with which to troubleshoot your memory interfaces.
>
>that can be helpful. I just use the CPU executing junk FF/00 or whatever
>else the bus lets it see,
This might work but is rarely predictable.
><After reading about the problems you're having, I think I'll fetch the 124
><LA out onto the patio as well.
>
>I troubleshoot 90% of my s100 problems with a good logic probe and
>a DVM. The rare case I've dragged out the scope it was handy but usually
>because I missed something stupid. The recent NS* bring up required the
>logic probe, its where I spotted a missing Mwrite/ (jumper smeared off the
>cpu board).
The logic analyzer is handy for gathering information about what a given
board does in a specific environment. I though I'd like to have pictures of
the cycle at the bus to correlate with the same cycle at the DRAMs, since I
have over a dozen DRAM boards to check out. This will give me information
about the various DRAM boards as well as the cycle timing generated by the
various CPU's.
>With rare exception and all if a board doesn't work scoping it may or may
>not help. just follow the logic with a logic probe as likely it's a chip
>or socket failure. The reason is the board worked, was sold working and
>if it were good it should still work. The exception is when you have bus
>incompatability problems and a scope will not help unless your going to
>alter the board to make it work assuming it was not also broken.
>
I've found the 'scope and LA more trouble to use than a meter and a logic
probe, but I've also learned that I get more useful information about DRAM
boards by looking at their DRAM control strobes and timing relative to the
memory access strobes and data than I could get with a meter and logic probe
under any circumstances. So many DRAM cards are at least partly timed with
one-shots, a tool which merely tells you sommething's happening but doesn't
tell you what, is not of much use in THIS case.
>
>Allison
>
Received on Wed Jun 02 1999 - 09:19:57 BST