Ref: 10630005
Title: GS/X.25 Clocking Configuration Mask Error on SIO-SMS Board
Date: 6/8/90

Copyright 3Com Corporation, 1991.  All rights reserved.

There is an error in the printed circuit board mask on the SIO-SMS board
in the GS/X.25-XNS and the GS/X.25-IP.  The error affects the SIO clock
configuration.

On the SIO board, areas E49, E69, and E70 determine whether the clock
sources are internal or external.  The mask for the area E70 is reversed
in the specification of "E" for external and "I" for internal clocking.
When setting these jumpers, use the following table and refer to the actual
shorting plug numbers.

Shorting plug settings for the SIO-SMS clock sources:

Port    Clock          Line    E49 Pins    E69 Pins    E70 Pins
No.     Source         Name    Connected   Connected   Connected
----    ------         ----    ---------   ---------   ---------
0       TX External    TXC        1-2*        1-2**       2-3*
0       TX Internal    EXC        2-3         1-2**       1-2
0       RX External    RXC        4-5*        n/a         n/a
0       RX Internal    --         5-6         n/a         n/a

1       TX External    TXC        7-8*        4-5**       5-6*
1       TX Internal    EXC        8-9         4-5**       4-5
1       RX External    RXC       10-11*       n/a         n/a
1       RX Internal    --        11-12        n/a         n/a

                             *   Factory default, user-alterable.
                            **   Factory default, not user-alterable.

The recommended settings vary according to the type of device being
attached.  In general, for use with modem equipment, both transmit and
receive clock sources should be set to external.  For direct connection,
the transmit clock should be set to internal and the receive clock to
external.
