There are many different ways to connect an 8870 to it’s VDUs, printers and the outside world in general.
The 8870 supports PLC (Programmable Line Controller) devices that provide a lot of interface options and protocols but for general connectivity of VDUs and modems, the ALME (Asynchronous Line Multiplexer Extended) is the preferred and easiest option. Even so, it also supports many different configuration options. The ALME itself can support Synchronous or Asynchronous operation and multiple BAUD rates and word lengths.
However at the physical electrical connection there are options as well, and these are controlled by the interface personality boards.
Be supper carful when removing or inserting the boards that have pins along the edge. The pins bend easily and if they are not perfectly aligned will snap off if you force the board into it’s socket. It was a good day when Nixdorf moved to boards that had sockets fitted instead of pins.
These boards fall into several categories.
IHSS – Inhouse
Most channels on an ALME will be fitted with IHSS boards with the exception of channels 0 and 1.
IHSS protocol is a robust hardware connection that allows VDUs to be located up to 1KM away from the main computer whilst utilising cheap 4-core none-screened cable.
The above board is a later generation IHSS with remote switch on (notice the relays). This board can be used within a BA80 VDU or an 1882-01 ALME. It will physically not fit in the older 1882-00 ALMEs or DAP4 VDU CPU boards as it uses sockets on it’s edge and not pins.
The above board is pretty much the original IHSS board. It has no remote switch on capabilities so would not normally be found in Channel 0 in an 1882-00 ALME, or in the Master Port 0 VDU. Notice it has gold pins along it’s edges. This board will physically not fit in a BA80 VDU or 1882-01 ALME.
The above board is a newer variant of the IHSS board. It’s basically identical to the previous IHSS board except the majority of components are now hidden inside metal screening cans. Again it has no remote switch on capabilities and will only fit the older DAP4 VDU processor boards or 1882-00 ALMEs.
* Notice that none of the IHSS board are configurable as IHSS requires no configuration.
The above is a basic V24 board and would typically be used in Channel 1 of the AMLE for connection to a modem. Notice how it contains no configuration jumpers or relays so again doesn’t support remote switch on.
This board can be used within an 1882-01 ALME and in theory can be used within a BA80 VDU though I’ve never seen it installed in one. Because this has sockets along it’s edges it will not fit in an 1882-00 ALME or DAP4 VDU processor board.
The above board is a V24 with remote switch on and would typically be found inside a DAP4 or DAP3 VDU. These cards are unfortunately easily damaged by leaking Lithium batteries in the DAP4 CPU board.
These circuit diagrams correspond to the original interface cards. The numbers relate to the pins on the card and you can trace these back to the 15 way connector on the ALME.