Path: utzoo!utgpu!news-server.csri.toronto.edu!bonnie.concordia.ca!ccu.umanitoba.ca!vspicer
From: vspicer@ccu.umanitoba.ca
Newsgroups: comp.sys.atari.st.tech
Subject: VME bus on the TT
Message-ID: <1991May24.140620.16320@ccu.umanitoba.ca>
Date: 24 May 91 14:06:20 GMT
Sender: vspicer@ccu.umanitoba.ca
Organization: University of Manitoba, Winnipeg, Canada
Lines: 20

Hello world
	I'm trying to interface a home-made data acquisition board designed
for an ST into a TT. I've made an adapter board which maps the VME pinouts
to their ST expansion bus equivalents so the existing board just plugs in.
The problem is that when I attempt to access the VME mapped memory area
(FE000000 base address) I get a bus error, 2 bombs. A logic analyser reveals
the AS* line on the VME bus isn't being set. I'm presuming that when I try
to access VME memory space:
	1- The address in question appears on the VME address lines.
	2- AS* changes to low to indicate the address is valid.
	3- An identity comparitor on my board sees that *AS, compares 
	   the address against a set bit pattern and engages the rest
	   of the board if they match.
The board DOES work on our ST machine, so the board isn't at fault. Shouldn't
AS* change state when addressing VME memory space? Or is there more to it
than that?

thanks in advance
		vic spicer
.