I have copies of the rs-232 and 485 standards.
RS-232 specifies both the electrical signals and the
connector type and pinout. The signals are "unbalanced."
RS-485 specifies only the electrical signal. Another
standard specifies the connector type and pinout.
I can't remember the name of that spec. Nobody seems to
use it anyway. The 485 electrical signals are "balanced."
Each signal uses a pair of signals for example T+ & T- or
R+ & R-. It is possible to have 32 receivers/tranmitters
on the signal although that depends on the 485 chip maker.
I belive that RS-232 specifies the bit sequence for data, parity,
stop, space, break. RS-485 is only a electrical spec.
More trivia... 485 is a differential driver and works great
for driving ethernet signals at about 10 meg. Check with the
chip maker. The protocols for ethernet are pretty stable.
You are probably on your own if you want a multidrop (party-line)
protocol for a serial port driving a 485 line with several
listener/talkers. Roll you own? or does anybody want to volunteer
some code for a serial port network??
Lou
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