Making a PS/2 Ethernet Adapter work in a 5494

The 5494 Remote Control Unit supports a Microchannel Ethernet LAN Adapter. This adapter can provide two different functions:

- It can connect twinax terminals (and PCs with twinax emulation cards) to 1-4 AS/400 systems connected to an Ethernet network; or - It can connect locally-attached Ethernet LAN systems to 1-4 AS/400 systems over the 5494's communication line 9V.24/X.21/V.35).

IBM supports ONE specific Ethernet adapter in the 5494 - PN 10H4633. This card is electrically identical to the IBM LAN Adapter/A for Ethernet, supported in PS/2 systems. However the Microchannel Card ID is different between the 5494 card and the PS/2 card, so putting a PS/2 LAN Adapter in a 5494 will not work.

The 5494 version of this LAN card nowadays is EXTREMELY rare. The PS/2 version of the same hardware is relatively obtainable still.

In researching the differences between the two cards, we discovered that the only difference between the two cards is the Microchannel Card ID, and discovered that it is possible - with some effort - to "renumber" a PS/2 LAN card to work in a 5494.

There are two PS/2 LAN card versions:

- A "long" card: https://www.ardent-tool.com/NIC/LAN_A.html#LAN_A-Old - A "short" card: https://www.ardent-tool.com/NIC/LAN_A.html#LAN_Adapter/A

It is possible to modify these cards to work in a 5494 by programming a new ID PROM chip. The chip on these boards is a small PLCC-20 pin surface mounted component and is non-trivial to remove and replace. However, both cards have a socket for an RPL/BOOT ROM chip that carries all but one of the required board signals, and the boot ROM is not used for the 5494 and needs to be removed anyway.

The basic hardware modification is not trivial, but not insurmountable for anyone with some soldering skills.

You will need:

- A soldering iron with a fine tip - Some solder (fine electronic rosin-core solver of almost any type) - Chip-Quik SMD Removal kit (optional, but helpful) - One 28 pin DIP chip socket (of the "square pin" variety, though the round ("machine pin") sockets will work in a pinch) - One programmable ROM chip of the 2764/27128/27256 type or any equivalent - A way to program the aforementioned PROM - Some fine wire, 28-30 gauge - An X-acto knife with a pointed blade or an extremely small bladed flat tip screwdriver