We did it! All five goals met.
Goal 1: Successful connection to TRS-80 Model 4 external bus. Done – thanks to an IDC50 breakout board which made the job easy. The slightly more difficult part was separating and identifying each line in the 50-pin ribbon cable and ensuring a match with the expected UBEC connections.
A permanent solution can be fabricated by hard wiring on a small perf board, or find a vendor to manufacture a TRS3 CBAC card (images of each circuit board’s trace layout are provided in the book).
Side note: The book describes much more than this blog post. There are DAC and ADC cards, a serial port RS-232 interface instead of the UBEC bus parallel interface and a number of model railroad specific devices. There are numerous examples of how to connect the CIN and COUT cards to a multitude of switches, motors, relays, displays, etc. Very comprehensive text.
Goal 2: Reconfigure UBEC for TRS-80 port I/O. Done as described previously. Not that hard given the detailed instructions in the book.
Goal 3: Update and repair the CIN and COUT cards. Done, and the boards function flawlessly.
Goal 4: Minor repairs to the IOMB and Test Card to ensure solid connections and no shorts. Done and continuity tests passed.
Goal 5: Successful execution of BASIC test programs to verify correct functioning of the hardware. Done as described in the previous post, for both the COUT card with LED test panel, and the wraparound test with COUT to CIN card.
The provided programs are easily modified for the type of I/O (port or memory mapped) and discuss ways to compensate for different “flavors” of BASIC. No issues with LS-DOS BASIC on the Model 4.
We now have a fully-functional vintage UCIS capable of putting a TRS-80 Model 4 to work sensing and controlling up to 48 real-world devices.
Kudos to the author, Bruce Chubb, for such an informative and well-thought out book that a self-taught hobbyist like me can understand.
Thanks also to the RetroChallenge team for inspiring me to embark on this journey!