RS422 and RS485 use the same differential signalling IIRC. The difference between two lines (>some mV <some mV) is what encodes zero or one. There's some allowed voltage range defined from ground but it's not that level that encodes the signal, it's the difference. Running a differential signal over a twisted pair reduces the noise.
In RS232, to contrast, the voltage defines the values, +/- 12V is also common and I think you can go pretty low while still meeting the standard.
ASCII is orthogonal, you can send anything over the serial link.
EDIT: apparently 3V-15V are the defined voltage levels (-3V - -15V) and drivers should tolerate up to +/-25V.
Big difference between RS422 and RS485 is the drivers for RS485 are required to survive a minus 7 volt difference between the two grounds.
Old R422 drivers would smoke if you got more than 7 tenths of a volt difference. Which would happen if you had a open ground. Or lighting hit. Or some big motor turned on. We had an RS422 based system with 50 units on one pair. One of them was holding the line. Coworker unplugged each one till he found it. And half of them didn't work after that.
In RS232, to contrast, the voltage defines the values, +/- 12V is also common and I think you can go pretty low while still meeting the standard.
ASCII is orthogonal, you can send anything over the serial link.
EDIT: apparently 3V-15V are the defined voltage levels (-3V - -15V) and drivers should tolerate up to +/-25V.