I am trying to connect a field device that has an RS422 to an RTU that has an RS485 port. This is a point-to-point configuration. Can these be connected directly? If no, how can they be interfaced?

Regards,
agoih

 

Do yourself a favor and read a little on the various communications standards.

http://www.arcelect.com/rs422.htm

 

Both types of interfaces are compatibles, they can be connected directly.

Check www.be-elec.com to download a booklet about RS-422/485 comunications.

Hope this helps.

 

B&B Electronics RS-422/485 Converter
Model # 4WSD9R

http://www.bb-elec.com

 

Here are a couple of things you might try. First, B&B Electronics makes a nice rs232/422 - rs485 converter.

http://www.bb-elec.com/product.asp?sku=485CSP2

</b>Another option might be to directly connect the two devices. If the rs485 is multidropped you won't be able to do this. Try connecting the rs422 TX to the rs485 RX+, and the rs422 RX to the rs485 TX+. I have found that this works pretty well as long as the cable distance is not too long (about 15ft).

Hope this helps.

 

The real question - is your RS-485 two or four wire?

Very likely RS-422 devices can be directly linked to RS-485 *FOUR* wire. In fact, I'd bet $$$ that your RS-422 device is using RS-485 chips since true RS-422 has some grounding problems that make it easy to damage. In fact, I don't think I've ever seen REAL EIA/RS-422 chips in any industrial devices.

However, if your RS-485 is two-wire, then you need to cancel the "echo" that a direct connection will cause. in that case, you'll need to use a true RS-422/485 converter which is really a "2-wire to 4-wire" converter. As mentioned, B&B sells one, as well as RDC which makes an isolated RS-485/422 repeater that can mix 2 & 4-wire: http://www.robustdc.com/library/PDFs/br485ir_v02.pdf

best regards
- LynnL, www.digi.com

 

You may also try CommFront's port-powered RS-232/RS-485/RS-422/TTL converters, used before, easy and reliable (2-year warranty).

http://www.CommFront.com