Are RS485 Full-Duplex interface same with RS422 interface?
\$\begingroup\$
\$\endgroup\$
2
-
4\$\begingroup\$ Could you share some context please? \$\endgroup\$– user17592Commented May 20, 2013 at 12:30
-
1\$\begingroup\$ Provide some background a good well written question will generate good answers, this question could use some work \$\endgroup\$– Voltage Spike ♦Commented Jul 6, 2017 at 15:14
Add a comment
|
2 Answers
\$\begingroup\$
\$\endgroup\$
1
RS-422 and RS-485 use the same electrical interface specification.
If you use that interface to build a bidirectional link on a single pair of wires, it's called RS-485, and it supports half-duplex operation.
If you use that interface to build two unidirectional links on two pairs of wires, it's called RS-422, and it supports full-duplex operation. This is sometimes mistakenly referred to as "full-duplex RS-485", but that's really a nonsense phrase.
answered May 20, 2013 at 15:35
-
\$\begingroup\$ You are the first person on the internet to clarify this explicitly. Thank you very much indeed. \$\endgroup\$ Commented Aug 6, 2019 at 14:20
\$\begingroup\$
\$\endgroup\$
3
RS-422 is a point to point communication connection. You can build it with one pair of wires to allow unidirectional communication between two parties (simplex, rarely used). With two pairs of wire it allows for bidirectional, duplex communication.
RS-485 is a bus structured communication setup that can potentially support multi master communication. It allows for multiple parties to communicate in full duplex if two pairs of wires are used. If only one pair of wire is present the communication flow is half duplex.
-
1\$\begingroup\$ Why would one use RS-485 with full duplex? You'll have one master that sends a message (with ID) and wait for the answer of that slave? If you'll send a message before that slave responds, there will potentially be two slaves talking on the line, which is bad. So sending and receiving shouldn't be at the same time, in a bus system? \$\endgroup\$– aaaCommented May 10, 2016 at 11:20
-
\$\begingroup\$ You would use it when the slave wants to talk continuously until asked to stop. With half duplex, the slave will have to release the line to see if master wants to say anything. With full duplex it does not have to do this. \$\endgroup\$– DojoCommented Feb 22, 2018 at 17:12
-
\$\begingroup\$ TI has a guide for it ti.com/lit/ug/sllu197/sllu197.pdf \$\endgroup\$– DojoCommented Feb 22, 2018 at 17:13