Serial RS232 mice could be connected to RS232 interfaces, such like the Amstrad Serial Interface, or to other (in-)compatible Serial interfaces (see Peripherals for a complete list of known Serial interfaces).
With their hardware based motion-counters, these mice would give much better resolution (5120 mickeys/second) (forty 3-byte packets/second) than the AMX Mouse (300 mickeys/second). Another approach to use a RS232 mouse would be a mouse interface like the AMX Kit, though that'd cripple the resolution to the AMX level.
Standard Serial Mouse (most common)
A serial mouse should be read at 1200 bauds, 7 data bits, no parity, 1 stop bit (7N1) with DTR and RTS on. For best compatibility, the mouse should output 2 stop bits (so it could be alternately also read as 7N2 or 8N1). When the mouse gets moved, or when a button gets pressed/released, the mouse sends 3 or 4 characters:
__First Character____________________ 6 First Character Flag (1) 5 Left Button (1=Pressed) 4 Right Button (1=Pressed) 2-3 Upper 2bit of Vertical Motion 0-1 Upper 2bit of Horizontal Motion __Second Character___________________ 6 Non-first Character Flag (0) 5-0 Lower 6bit of Horizontal Motion __Third Character____________________ 6 Non-first Character Flag (0) 5-0 Lower 6bit of Vertical Motion __Fourth Character (if any)__________ 6 Non-first Character Flag (0) 5 Middle Button (1=Pressed) 4 Unused ??? 3-0 Wheel ???
Additionally, the mouse outputs a detection character (when switching RTS (or DTR?) off and on:
"M" = Two-Button Mouse (aka "Microsoft" mouse) "3" = Three-Button Mouse (aka "Logitech" mouse) "Z" = Mouse-Wheel
Normally, the detection response consist of a single character (usually "M"), though some mice have the "M" followed by 11 additional characters of garbage or version information (these extra characters have bit6=0, so after detection, one should ignore all characters until receiving the first data character with bit6=1).
Mouse Systems Serial Mouse (rare)
Accessed at 1200 bauds, just like standard serial mouse, but with 8N1 instead 7N1, and with different data bytes.
__First Byte_________________________ 7-3 First Byte Code (10000b) 2 Left? Button (0=Pressed) 1 Middle? Button (0=Pressed) 0 Right? Button (0=Pressed) __Second Byte________________________ 7-0 Horizontal Motion (X1) __Third Byte_________________________ 7-0 Vertical Motion (Y1) __Fourth Byte________________________ 7-0 Horizontal Motion (X2) __Fifth Byte_________________________ 7-0 Vertical Motion (Y2)
The strange duplicated 8bit motion values are usually simply added together, ie. X=X1+X2 and Y=Y1+Y2, producing 9bit motion values.
Notes
Mice do return raw mickeys, so effects like double speed threshold must (should) be implemented by software.