RS485 signal ground pin

[Andrey]

Controller^ V570-57-T20B

COM 2 configured as RS485/

Pin 1 is the "A+" signal.

Pin 6 is the "B-" signal.

 

What has "signal ground" pin? 2 or 5 ?

 

[cantcliff]

RS-485 is a two wire differential protocol for the Vision series. 

 

There is no signal ground.

[Andrey]

https://en.wikipedia.org/wiki/RS-485

 

Please read the section named as "connectors".

IMHO: network without SG (signal ground) worked very bad.

[AlexUT]

Hi Andrey,

Following is a link to Unitronics document http://www.unitronics.com/docs/technical-library/unitronics-devices-and-rs485.pdf "Unitronics Devices and RS485".

It explains in details RS485 wiring.

I hope this helps.

[cantcliff]

https://en.wikipedia.org/wiki/RS-485

 

Please read the section named as "connectors".

IMHO: network without SG (signal ground) worked very bad.

 

Andrey,

 

Typically yes, if you use 0v as your reference.  RS-485 two wire uses the voltage differential between A+ and B- as it's reference on a twisted pair wire.  The biggest advantage is both wires would be prone to the noise.  So if A+ is offset, B- is also offset by an identical amount and the differential is maintained.

 

There are also a 3 wire spec, and a 4 wire spec (4 wire is used for full duplex communication).  As always, you should still use grounded cable with the ground connection on one end to improve performance and minimize noise.