This is a multifunction card that contains a clock, a parallel port, and a serial port. There is also 256 bytes of battery-backed SRAM that stores the card configuration. The manual is nice in that it describes all the registers and how to use the card’s hardware directly.

This card has the ability to make the I/O devices appear as “phantom” devices in any slot. It does this by decoding the full address bus (instead of just using /IOSEL) and U25, configured by the host CPU, decides if the slot being accessed should be handled by the card. The manual describes that pin header J6 is also used with a companion board that replaces an IC on the main logic board to help with this “phantom slot” feature. I don’t have this board so I’m not able to capture its schematic.

It’s not clear what the SRAM chips being used are but they appear to be mostly pin-compatible with 2114 SRAM chips.

Schematic

KiCad Project & all artifacts

Front Image

Back Image

Note: There is supposed to be a 2xAA battery holder attached to the back but mine had broken off so this photo shows just the PCB.