>
>At the receiver:
>
>Anything below -3v is a mark.
>Anything over +3v is a space.
>
>Anything in between is 'invalid'.

True enough, but look at the circuit for the 1488/89 receivers.
They can only see positive voltage.

>At the transmitter:
>
>Send -5v (or -6v?) to -15v (or -30v? or ??) for  a mark.
>Send +5v (or +6v?) to +15v (or +30v? or ??) for a space.
>
>(does anybody know with assurance the correct range on the transmitter
>side?)


I don't think they spec it that way. They define a standard load, and it's
up to you to deliver the goods.

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