Continue to Site

Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Register Log in

[SOLVED] does rs422 need ground?

Status
Not open for further replies.
A

asadi.siyavash

Member level 4
Joined
Feb 14, 2013
Messages
68
Helped
2
Reputation
4
Reaction score
2
Trophy points
1,288
Activity points
1,769
Hi as I know RS485 full duplex, doesn't need ground but in some sites I saw that someone used "RS422" with 4 connection and some of them 5 connection(4data + ground).
which one is true?
all the best
Siyavash
 

RS-422 needs the two ends' grounds to remain within +/-7V
to meet input common mode range on the receiver. A hard
wired ground would enforce this, at the cost perhaps of
some longitudinal current or ground loop. In a fairly close
assembly perhaps an implicit ground relation can be assumed
but this assumption wants checking in each case.
 
RS485 is the same. A direct ground connection isn't essential as long as you can guarantee the differences between each end is small enough. I would always advise you DO use a ground to be safe. Even if the two (or more) ends measure low ground voltage differences on a test meter the link will still be prone to interference.

Brian.
 
RS485 or RS422 with isolation don't need a ground wire, review the specification of respective interface standards like PROFIBUS. But if non-isolated, a ground connection is required to keep the common mode voltage within safe limits.
 
The problem with RS-485 in full duplex is cross-talk from CM coupling of signals. To get good performance a ground wire helps absorb stray CM noise and a good CM choke helps even more. Data wires should be balanced such as CAT5 or twisted pair with proper impedance terminator matched to cable impedance.
 

really thanks as I saw in application note and datasheet of non isolate part like ADM3490 analog devices, it doesn't use any ground connection even for it's evaluation boards. but I got that in some cases some manufactures used ground. so with your answered I understand using ground improved performance. also there is no difference between RS422 and RS485 in this case.
 

Status
Not open for further replies.

Similar threads

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top