Ref: 15990016
Title: Problem Using Telebit Modems with PFAIL.SYS File Installed
Date: 2/27/90

Copyright 3Com Corporation, 1991.  All rights reserved.

You will experience problems using most Telebit modems on COM1: of
3Server386s when you have the PFAIL.SYS driver installed.  This article
explains the problem and gives you workaround options.

PFAIL.SYS is used with an Elgar or compatible UPS (uninterruptible power
supply).  It monitors pin 13 of the COM1: port of the server on which it is
running.  The UPS will maintain a negative nine volts on this line during
normal operations.  When power failure is detected, however, the UPS brings
pin 13 to positive nine volts, therefore informing PFAIL.SYS that power has
been removed.  After a short time the PFAIL.SYS driver will broadcast a
shutdown message and gracefully shut down the server.  The last action it
takes is to raise pin 19 to tell the UPS that it can turn itself off.

The conflict is that pin 13 is defined as "Secondary CTS," and the Telebit
modems make use of this.  They have the capability, which 3Com does not use,
to have multiple communications channels implemented on pin 13.  The Telebit
modem will hold this line high at all times the modem is ready to receive.
Unfortunately, the Telebit modem use of pin 13 interferes with PFAIL.SYS,
because it expects pin 13 to be low.  As a result, the server will go into
shutdown mode as soon as it comes up.

If you are not using an Elgar or compatible IPS with the LanSafe cable
installed, remove PFAIL.SYS from your CONFIG.SYS file on the 3Server386,
Otherwise, you can choose not to attach the Telebit modem to COM1: or not
to bring pin 13 through from the modem to the server.  Unfortunately, there
is no way to tell the Telebit modems not to hold pin 13 high.

