Monday, November 24, 2003

RS422 over cat5 cable
I cable a lot of TV facilities and the tendency nowadays is to use the ubiquitous cat5 data cable for carrying everything that doesn't require a better grade of cable. RS422 for machine control used to be universally carried on Star Quad cable but now cat5 does the job - here is the pinout I have settled on:

  • I avoid the blue pair because that is often used to analogue voice and if you mis-patched you may wind up terminating a data pair in a low impedance.
  • The brown pair often carries power in POE (Power Over Ethernet) implementations and if you mis-patch the sending switch sees a low impedance and shuts off the current.
  • The orange and green pair carry the Tx and Rx pairs as per ethernet (which expects to see a 110 ohm termination).
That's why I do it thus!

2 comments:

rudyboxing said...

Hi Phil

Do you have any of photos of this would be great

Phil Crawley said...

Well since this post was from more than ten years ago I have changed how I do RS422 a bit!
http://philtechnicalblog.blogspot.co.uk/search/label/RS422
Bit more reading! It's a robust signal standard and so it probably comes down to local standards - Probel, Evertz etc.