Here I use a cheap, basic USB logic analyser to reverse engineer part of the custom firmware permanently built in to the ROM of the Texas Instruments TMS1600 microcontroller at the heart of the Busch Microtronic 2090 Computer System.
In this video I validate the mapping used by the OPLA, or output programmable logic array, which is used to map a four-bit data value (plus status bit) to a Microtronic specific pattern on the eight O-output pins.
The Microtronic uses the OPLA to control the display and, in part, to address the RAM. While we can compare the retrieved ROM code with what the Microtronic displays on the LEDs to figure out the display mapping, the pattern used on the O pins when it is accessing RAM cannot be inferred from the code alone...
8-channel USB Logic Analyzer: https://www.aliexpress.com/item/1005006004951378.html
Mini Grippers: https://www.aliexpress.com/item/1005007537747320.html
PulseView software: https://sigrok.org/wiki/PulseView
For more information about the Busch Mictrotronic 2090 Computer System, check out Michael Wessel's YouTube channel.
https://www.youtube.com/@michaelwessel4953
Michael's Microtronic projects
Retro-Authentic Microtronic: https://hackaday.io/project/180252-a-retro-authentic-microtronic-rc-202110-winner
PicoRAM 2090: https://hackaday.io/project/192655-picoram-2090-retrochallenge-202310-grand-prize
Microtronic Firmware: https://hackaday.io/project/197415-microtronic-firmware-rom-archaeology
Busch Mictotronic 2090 Computer System
Official website: https://www.busch-modell.de/information/Microtronic-Computer.aspx
Quick reference card: https://github.com/lambdamikel/Busch-2090/blob/master/manuals/anl2090-0.pdf
Schematic: https://github.com/lambdamikel/Busch-2090/blob/master/manuals/microtronic.jpg
Texas Instruments TMS 1000 Family Data Book
https://archive.org/details/tms-1000-family-microcomputers-data-book_202208/
More details about our adventures reverse engineering the Busch Microtronic 2090 Computer System can be found here.
https://hackaday.io/project/197415-microtronic-firmware-rom-archaeology
https://jsonj.co.uk/project/microtronic/