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TL;DR: This PR fixes the UART i8274 chip connections to the GRiD Compass laptop and also fixes Microsoft Mouse.
GRiD Compass and Serial
The GRiD Compass uses a proprietary 19-pin connector that provides RS232, RS422, and +10V/-10V power. The circuit uses PAL chips that configure the signal source for TxC, RxC, and also SC for GPIB. There's no PAL dump available, only some circuit diagrams and approximate connection descriptions from @ConventionalMemories and @JDat...
Instead of emulating the PAL chip logic, I connected the i8274's TxC/RxC directly to 80130 baud. I also fixed the swapped
cdbapins, set the correct i8274 address for the GRiD Compass II and configured interrupt.Additionally, I updated the device list. It now includes a simple serial printer (without software flow control) that works with the
MinimumSerial~Printer~driver, plus two mice: Microsoft Mouse and Logitech Mouse. Both mice only work in GRiDPaint. On macOS, both mice behave erratically, but this appears to be a broader MAME issue on macOS rather than an emulation problem. The Mouse Systems mouse is commented out because it doesn't work for some reason.Video showing the mouse working on this branch:
Screen.Recording.2026-03-12.at.15.08.35.mov
Microsoft Mouse fixes
The Microsoft Mouse had incorrect Stop Bits setting — 2 instead of 1. Also, the DCD and CTS lines weren't set, which prevented the mouse from being detected in GRiD OS 3.1.5. I didn't create a separate PR for these three lines, but if this change needs separate review, I can move the commits to a different branch at the maintainers' discretion.
P.S. My goal isn't to achieve perfect Compass emulation — I just want to make GRiD OS 3.1 programs work correctly without obvious artifacts in MAME.