Mits Altair 88-2 SIO Rev 0

I need to ascertain whether this is an A RS-232, B TTL levels or C current loop

--Jeffa (talk) 11:04, 19 May 2015 (CDT) I replaced the broken capacitor. Placed the 88-2 SIO in my Imsai test system. Survey.com reports I/O ports 10, 11, 12 and 13 hexadecimal which relates to markings on board Port 17 19 assumed in octal. Status then data ports hence the odd numbers. Guess I'll break out the oscilloscope to verify it's RS-232 rather than current loop or TTL levels.