RS-422 Splitter? Hub? Help!

One of our operator consoles has a keypad that is connected to a PC using RS-422. We use to account for downtime, and at the end of the shift, the PC prints off a report. I have set up a web page on our company intranet that shows relevent PLC production data to anyone in our company who is interested.

My problem is that I would like to include the reasons for the downtime in this web page. I am still researching it, and starting to get somewhere, but I thought if anyone had a similar experience already it would really help out. I've found a RS-422 to 4-20 ma current loop adapter fot $80 to tie into our PLC 5/40E, but I haven't found a way to "tap in" to the data coming from the keypad yet. Everytime the downtime clock starts, the operator has to punch in a number between 1 and 15 to account for the cause of the downtime.

Can you simply use a Y-splitter to "eavesdrop" on the Keypad to PC communication, or do you need a hub and some knid of network configuration?

Thanks,

Vetteboy

I have tied the RX line in parallel on a RS232 port to tap data off to monitor ASCII data in the past. I'm guessing that could be done on the RX lines for the RS422 for monitoring, using a Y splitter.

So there wouldn't be a problem with splitting the signal, and then tying the RX to the PLC? I seem to be having trouble finding a Y-splitter for RS-422, leading me to believe you aren't supposed to do it.

You could always convert the 422 to 485 then split that, like this:
http://www.baudmaster.com/bm-app4.htm
Look at Y networks.

B&B Electronics also makes converters for things like this
http://www.bb-elec.com/

Thakns RS, I was at the B&B site but hadn't seen the other one. The only problem I see is that all of these convert TO 422 not FROM it. Maybe I'm blind......

Vetteboy

If you look at the Y network picture, the first link, it will show you RS232, 422 or 485 going in and out. Between the adapters is RS485. With these apapters communication is bidirectional..ie RS232, 422 or 485 can be on the equipment side.

Basically what it would amount to is setting up an RS485 network. In this case when the keyboard transmits a signal then you could use another device, to as you said eavesdrop, and read the signal.

Here is an example of a splitter.....

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RS232 is designed for point-to-point communication with only 1 driver and 1 receiver on the same line, but as jrwb4gbm wrote, it should be possible to have 2 receivers (RX) on the same line if you want to listen/record e.g. using a data-analyzer.

RS422 was designed for 1 driver and up to 10 receivers on line, but I often see spec. with up to 32 receivers.

RS422 and RS485 have many similar characteristics, but RS485 is designed for up to 32 drivers and 32 receivers on line
(A RS422 driver is normally a dual-state driver while a RS485 driver is a tri-state driver)

Read e.g. this URL: http://www.analog.com/UploadedFiles/Technical_Articles/484300879InterfacePrimer.doc

So the answer to Vetteboy is: You can connect several receivers to one driver (from the operator console). You don't need any RS422/RS485 converter if you only need an additional receiver. (If you need several drivers, then you need RS422 with tri-state or a converter to RS485)

If you have full duplex communication between your operator console and the PC and put a RS422/RS485 converter between, then the
communication is reduced to half duplex.... that is: you can't send and receive at the same time.
Besides, the converter also cost money...

Use a terminal strip instead, but avoid long stub cables

regards