Re: RS485 is bidirectional does it mean it is fullduplex?

"Tim Mitchell" <timng@xxxxxxxxxxxxxxxxxxxxx> wrote in message
news:uAXCZAWeYCsCFAHz@xxxxxxxxxxxxx
> RS485 is a 2-wire half duplex system where there is one transmitter and
> multiple receivers.
>
> RS422 is a 4-wire duplex system which goes between two devices, each of
> which has a transmitter and receiver.

While this is essentially correct, I'd add:
- Don't forget ground - i.e. 2-wire is actually 3-wire, and 4-wire is
actually 5-wire.
- RS-422 is also multidrop (10 max drops, IIRC).
- RS-422 is often implemented using a pair of RS-485 devices these days,
since the RS-485 spec is superior to the original RS-422 spec. This confuses
things slightly, but means that RS-485 tends to be used in both 3-wire and
5-wire configurations.

Finally (pedant mode on), the old RS-422/485 appellation is obsolete:
strictly speaking it's now EIA-422 and EIA-485. (This may be useful to know
for Googling purposes.)

HTH,

Steve
http://www.fivetrees.com


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Relevant Pages

  • Re: RS485 is bidirectional does it mean it is fullduplex?
    ... >> RS485 is a 2-wire half duplex system where there is one transmitter and ... >> multiple receivers. ... >> which has a transmitter and receiver. ... signal ground connection. ...
    (comp.arch.embedded)
  • Re: RS485 is bidirectional does it mean it is fullduplex?
    ... >> RS485 is a 2-wire half duplex system where there is one transmitter and ... >> which has a transmitter and receiver. ... "fail safe" resistors will force the receiver power supply Vcc and Gnd ... The RS-422 impedance levels allows for multiple receivers, ...
    (comp.arch.embedded)