Saved the following as a useful referance in case others were looking for it - my thanks to Jim Brain for the info:
Craig Taylor wrote:
> Jim Brain wrote:
>> Craig Taylor wrote:
>>> Does anyone know how the A/B switch on this works? Which pins it comes
>>> out on / how it selects different RS232 devices? (I assume that is it's
>>> purpose?)
>>> - Craig Taylor
>>> http://www.ctalkobt.net/cbm
>> I have one of those, but mine has 3 switches, no A/B switch.
>> Jim
> I should have looked at it before posting.
> Mine has 3 switches also:
> Modem1 / Printer 1
> Modem2 / Printer2
> Normal / Inverted
> Now, the normal / inverted I know of it's use but how does it
> distinguish between the Modem1/Printer1 or Modem2/Printer2 switches?
> What do they actually do?
> - Craig Taylor
> http://www.ctalkobt.net/cbm
To be 100% sure, I'd have to hook it up and check again, but from memory:
M/P1 switches from DTR/DSR signaling to CST/RTS signalling
M/P2 hooks CTS to RTS on same side (nulling them out)
Normal/Inverted inverts DTR/DSR.
Jim