trs 80 model I "i/o bus interface adapter"

I don;t have one, I never had a hard disk on my M1. But I can try a few guesses The hard drive units for the M3/M4 consised of a drive, a Western Digital controller (WD1001 type thing) and a simple address decocder. The drive unit had a cable that plggued into the M3/M4 expansion bus connector. Said bus allowed you to add external I/O-port devices, and conssited of 8 addres lines, 8 data lines and a few control lines It's a 50 pin edge connector. The M1 bus has rather more signals (and fewer grounds) on a 40 pin connector. Most of the M3/M4 signals are there, just on different pins. One mino differnce is that the M3/M4 requires the peripheral device to pull a pin low o nthe connector when it's being accessed, to enable a buffer inside the computer, The M1 has nothing like this. Anyway. My first guess is that the adapter boes between the 40 pin expansion bus of the M1 (front connector on the left side of the EI) and the 50 pin cable to the hard drive controller. It simply connects the signals on the cable to the right pins on the M1 bus. Given the pinouts (and they're in the technical manuals for the M1 and M3), it shouldn't be hard to make something. -tony