In a MegaST2, I found a expansion board on the VME bus.
It outputs 2 DB9 (1 male, 1 female).
The card is pretty simple. The main chip, SCN68681C1N40 is a "Dual Universal Asynchronous Receiver/Transmitter (DUART)"
It takes its power from the free connector on the motherboard.
The board name is BNC 100 ST V3.0 8815
It come from a UK MegaST2, TOS 1.02, without blitter

Here a picture : Anybody knows it ? It seems to be a Germain board (red sticker on top).