Date   : Sat, 25 Apr 1981002:36:00-MST
From   : Keith B. Petersen <W8SDZ@MIT-MC>
Subject: [W8SDZ: Northstar/modem conflict]

Date: 25 April 1981 04:32-EST
From: Keith B. Petersen <W8SDZ>
To:   MMD at SU-AI
cc:   BUG-MTN, W8SDZ
Re:   Northstar/modem conflict

This is not an "official answer" from BUG-MTN, but I noticed your
message there and wanted to pass along a bit of info you may find
useful.  If you are using a Horizon mainframe, you cannot use port C0H
for the PMMI modem.  The reason is that that port is used by the
mother board for some sort of parity business with Northstar memory.
Everyone I know who has a Horizon II has had this problem.  It doesn't
seem to matter whether you have the parity option on your memory
boards or not.  The symptom is unexplained bombing of programs used
with the modem.  Anytime the program does an output to port C0H, it
messes up the system memory.
   Around here, Horizon owners have standaradized on port B0H.