I am looking for an RS422 Device?

[jwhitmore]

Hello all, the subject sort of sums it up but I may well have missed that boat. I'm playing with/learning about RS232, RS422 and RS485 and would like to interface with devices using all of them. RS232 and RS485 as I already have devices that talk using those physical interfaces. RS422 however seems to have slipped away. A search on eBay will throw up any number of interface devices which will convert an RS422 device to USB or whatever but nothing seems to actually use it. I guess given it's a bit more complicated then the other two nobody uses it for simple temp sensors or whatever.

I guess I could create two ends of an RS422 interface with a PCB design but both ends could be wrong and I'd never know. If I had something which I was fairly confident was communicating properly and I could communicate with it I'd feel happier.

Any thoughts or let it go? I assume that there's a load of 422 legacy kit still used in industry?

[Paul Moir]

RS422 has the same signalling as RS485, just without the ability to have multiple transmitters.  Think if it as RS-232 with RS-485 signalling.  So you just use a RS-485 driver for it.
(Minor note:  RS-422 allows for multiple receivers.)

EDIT:  That's somewhat wrong:  they are slightly different in signalling, but I think transceivers use the spec overlap.

[SL4P]

...and is often implemented as 4-wire full duplex (effectively balanced RS-232)

[NW27]

RS422 can also have multiple transmitters and receivers.
The significant difference between RS422 and RS485 is RS422 uses four wires (2 for tx and 2 for rx) and is full duplex ie it can receive at the same time that it is transmitting.
RS485 uses 2 wires only and is therefore half duplex.
You can use RS485 chips to create a RS422 network. As an example of the PC end, set one RS485 chip as a constant transmitter (output enable is a separate thing) and the second RS485 chip (again still at the PC end) as a constant receiver.
This gives the four RS422 wires at the PC end.
Do similar for the remote end.
Also the lines should be terminated and preferably pulled to a known state

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[hendorog]

Worth noting as well that you can connect  RS422 device(s) to RS485 device(s) - obviously this means the network, and the 422 devices, need to operate half-duplex.

[jwhitmore]

Thanks for all the advice it's probably not the best solution but I've laid out a board with 2 x SN65HVD72D chips. I can use one of the for half duplex RS485 and use both for full duplex if I find something to talk to.