Ref: 03190012
Title: 3C503 and 3C503-TP Adapters Incompatible with IBM Model 25/286
Date: 12/31/90

Copyright 3Com Corporation, 1991.  All rights reserved.

Certain versions of the IBM PS/2 Model 25/286 will not boot with the
EtherLink II or EtherLink II-TP adapter installed.  The problem is caused by
a glitch in the Model 25/286 AT-bus.

The Model 25/286 was introduced by IBM in June 1990.  It is a 10MHz
80286-based machine with two AT expansion slots.  The Model 25/286 bus IORD
signal generates a 3-5 nanosecond glitch toward the end of a clock cycle.
The glitch causes the EtherLink adapters to think that a new clock
cycle has started when it has not.  The glitch is not supposed to occur,
according to the IBM Technical Reference Manual.  3Com is in contact with
IBM engineers to resolve the problem.

The problem appears only on the Model 25/286 with EtherLink II or
EtherLink II-TP.  EtherLink and EtherLink 16 adapters work fine with the
Model 25/286.  Other PS/2 models--including the Model 25, Model 30, and
Model 30/286--work fine with either adapter.

