[cctalk] Endeco Cartridge Reader

Is anyone familiar with the Type 1138SSM Cartridge Reader by Endeco, Inc (of Marion, MA) ? I recently got one, it appears to have an RS-232 interface at the back (and a power cable). I believe it is from around 1989. The cartridge slot has a connector that looks like something an NES might have. That is, it is not a tape, but it is much larger than CompactFlash. If anyone is familiar with these, I'm trying to find some cartridges and any kind of manual on how to interface with the thing. Thanks! Steve