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From: ian@sibyl.eleceng.ua.oz.au
Newsgroups: comp.sys.nsc.32k
Subject: Hardware Problems
Message-ID: <9006041632.19186@munnari.oz.au>
Date: 4 Jun 90 02:51:59 GMT
Sender: news@daver.bungi.com
Lines: 39
Approved: news@daver.bungi.com

My board occasionally gets into a stuck state, where "reset" fails to
restart things.

When it is in this state, the LED's are out and the CPU is stopped
with /rdy high. It appears to stop in a write to the AIC6250 or at
least with /scsi selected. I've measured the signals around the WAIT
PAL a DVM which is not the most appropriate instrument, but its the
best I have at home.

		U38
	Pin		Logic Level
      -----------------------------
	1 (ck)		Pulsing (*)
	2 (/eprom)	1
	3 (/scsi)	0
	4 (/bmt)	1
	5 (/ddin)	1
	6 (/slow)	1
	7 (drq)		0
	8 (scsii)	0
	9 (a22)		1
	11 (/oe)	0
	12 (/dack)	1
	13 (/nrdy)	0
	14		1
	15		1
	16		1
	17 (/rd)	1
	18 (/wr)	1
	19 (/eop)	1

* I measure an intermediate voltage so I presume there is clock present.

This fault is difficult to reproduce. This state is *after* I have pressed
reset, however, reset normally does the write thing. Is there some flip
flop somewhere which should be reset and isn't? I have no idea if this is
a design fault or a fault on my particular board.

Ian Dall