Ref: 09930005
Title: Shared Memory Settings for Etherlink Start PROM
date: 2/21/90

Copyright 3Com Corporation, 1991.  All rights reserved.

The Shared Memory Base Address determines the memory location of
the optional EtherStart PROM installed in the Etherlink adapter
(3C501).  You can select base address values from 00000H to
FF000H in 4 KB increments.  The factory default setting is EC000.

If you are using an IBM PC or XT, you can use the base address
values C8000 to F3000.  If you are using an IBM AT, you can use
the values C8000 to DF000.

If the optional EtherStart PROM is installed, you must set the
Memory Enable jumper to 1.  Refer to your Etherlink manual to set
the Memory Enable jumper.

To change the 20-bit address for the EtherStart PROM, you can ONLY
change the top 8 bits of the address.  The last 12 bits are always set
to 0.  The default settings are

   Jumpers ON the board               Jumpers NOT on the board

19  18  17  16   15  14  13  12     11 10 9 8  7 6 5 4  3 2 1 0

 1   1   1   0    1   1   0   0      0 0 0 0   0 0 0 0  0 0 0 0
               |                 |           |         |
      E        |       C         |     0     |    0    |    0

Address: EC000


The following table can be used to set the top eight bits in hex.

     0000    0      0100    4      1000    8      1100    C
     0001    1      0101    5      1001    9      1101    D
     0010    2      0110    6      1010    A      1110    E
     0011    3      0111    7      1011    B      1111    F


Note:  A legend labeled "Jumpers" is provided on the Etherlink
adapter.  This diagram displays the position that a jumper must
be placed in to indicate a value of one or zero.

