Hi Bob...we don't need no steekin oscilloscope! Have multimeter will travel!
I'm looking up the Gemini IC chips to determine the RS232 interface.
I can drive Gemini thru
Gemini ASCOM. It's kinds like EQMOD but different. It's a standalone driver that can also be used with planetariums etc.
edit:
RS232 interface looks like a MB3221 (Max3221) chip which is EIA232, 3-5V logic compliant.