


Hardware installation


This section describes problems that may arise in the use of
local area network hardware in the IBM PC.


Memory expansion card flaw

Some IBM 64K/256K memory expansion cards have a design flaw that
causes trouble when an I/O device uses DMA channel 1.  (The PC/IP
software usually uses DMA channel 1 for the Ethernet or the
Pronet.)  The symptom of this design flaw when running PC/IP
software is a catastrophic crash with the screen displaying the
message "PARITY CHECK 2".  The crash usually occurs within the
first hundred or so packets transmitted to or from the network.

If this problem appears, one should check the memory expansion
card to see whether or not it has this design flaw, and whether
or not it has been field-upgraded.  Flawed cards have a
connection between pins nine and ten of chip U49.  (The
connection is a very small printed circuit stripe on the
underside of the card.)  Repaired cards have had that connection
severed, and two new wires added, from chip U33 pin eight to chip
U33 pin eleven, and from chip U33 pin ten to chip U49 pin nine.
Note that making changes such as these must be done with care to
avoid damaging the card, and may void any warranties.  If you
have a flawed card it may be appropriate to inquire of your
dealer what action should be taken.  Alternatively, the network
can be operated using DMA channel 3 if that channel is not
already in use for some other device such as a hard disk.



Ethernet jumper selection

There are several jumper-selectable hardware options on the 3COM
Etherlink Ethernet card.  The cards come in two forms.  The
first, older form, is identifiable by the label "Rev. A" or "Rev.
x.y" where x and y are integers.  The second, newer form, is
identifiable by the label "Rev. B" and by the presence of a
humongous, 64-pin chip in the upper left corner of the card (when
held with the chips visible and the bus connector pointing down.)
The two kinds of cards have completely different labels for their
option setting jumpers, and the newer cards have a few additional
settings.  The option set at the top of the next page is known to
work with the PC/IP Ethernet packages.

The choice of which DMA channel and which interrupt vector to use
depends on what other I/O equipment is attached to the PC.  For
example, on an IBM PC/XT the hard disk, floppy disk, and printer
are configured to use interrupt vector positions five, six, and
seven, leaving two, three, and four for other attached devices.
The Ethernet commonly uses interrupt vector position three.

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3COM Etherlink card option settings:

    Rev. B             Rev. A
    label              label       suggested jumper position
DMA REQ                 jp1    channel 1 (must match software)
DMA ACK                 jp2    Must match DMA REQ or jp1
Interrupt               jp3    vector 3 (must match software)
I/O address bit 9       n/a    right (1)
I/O address bit 8       jp4    right (1)	
I/O address bit 7       jp5    left  (0)	
I/O address bit 6       jp6    left  (0)	
I/O address bit 5       jp7    left  (0)	
I/O address bit 4       jp8    left  (0)	
Memory address bit 19   n/a    right (1)
Memory address bit 18   jp9    right (1)	
Memory address bit 17   jp10   right (1)	
Memory address bit 16   n/a    left  (0)
Memory address bit 15   n/a    right (1)
Memory address bit 14   jp11   right (1)	
Memory address bit 13   jp12   left  (0)	
Memory address bit 12   jp13   left  (0)	
Memory enable           jp14   right (disable)
n/a                     sw1    Left for onboard transceiver,
                               right for external transceiver
U11/U10                 n/a    Plug goes in socket U10 for onboard,
                               socket U11 for external transceiver

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(Note that older Etherlink cards can be set only to interrupt
vector positions three and five, and therefore must use position
three in an XT.) Similarly, the PC/XT uses DMA channel three for
the hard disk and DMA channel two for its floppy disk, so the
Ethernet must use DMA channel one.  (Note that in recent
shipments the 3COM Ethernet card has been configured at the
factory with exactly these two settings.) 


Pronet jumper selection

There are both switch-settable and jumper-selectable options on
the proNet p1300 ring interface.  Section three of the "Operation
and Maintenance Manual" should be consulted for details.

a)  Switches.

The node address switch (S39) must be set to an address different
from every other station on your ring network, and that address
is the same as the value in the last field of the internet
address that your machine has been assigned (see step one under
software installation.)  Note that the node address switch uses
the "on" position to denote the binary value "0" and the "off"
position to denote the binary value "1".  The board/rom address
switch (S22) should be set to all zeros (all "on".)

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b)  Jumpers.

The interrupt vector jumper and the two DMA jumpers (one for
input, one for output) must agree with the configuration that the
software will assume, and must not conflict with other installed
I/O devices.  The card can be set to use any of interrupt vector
positions 2, 3, or 4, and any of DMA channels 1, 2, and 3.  The
PC/IP software requires that the two DMA jumpers be configured to
use the same DMA channel.  The card is usually shipped with the
jumpers set for a configuration that will work with a standard PC
or PC/XT, using interrupt vector 2 and DMA channel 1 for both
input and output.



21 November 1984.  This document is in file hardware.txt
