485onCAT5?

[MOUNTAIN747]

I have a working board to gather 1-wire com and sent it to PC via RS232. I would like to modify my board to include a RS485 output. I think I have figured out how to implement the RS485 in full duplex without having to change any of my current code but I have a few of questions.
(1) If I parallel my RC6/TX and RC7/RX from my 16f873 both to the MAX232 and my SN75179B(RS485), will the 16f873 be able to drive both devices or should I place a buffer on the output of the f873? I am not sure how to make that determination.
(2) I am going to use CAT5 wiring to deliver the RS485. I am not clear about the use of each twisted pair to deliver the full duplex signal. One article I found said to use a wire for SN75179 signal “A” in one pair while using a wire for signal “B” in another pair. Does that mean I can use one pair to carry signal “A” & “Y” and another pair to carry “B” & “Z”. I would like to use a third pair to carry a momentary push button signal on the RS485 cable.
(3) Unused wires? Should any unused wire in the CAT5 cable be grounded, and is it a bad idea to run 5V in the same cable? Comments will be appreciated.

[falingtrea]

For RS485, the TX and RX pairs should be on seperate twisted pairs (RX and RX* on one pair and TX and TX* on on other pair).

If you parallel two types of line drivers, you need to have some way to disable the RX on each. Otherwise they will fight against each other.

Power over Ethernet does supply power over the same cabel as the signal. so as long as you take in account the voltage drop you should be ok.

[MOUNTAIN747]

For RS485, the TX and RX pairs should be on seperate twisted pairs (RX and RX* on one pair and TX and TX* on on other pair).

If you parallel two types of line drivers, you need to have some way to disable the RX on each. Otherwise they will fight against each other.

Power over Ethernet does supply power over the same cabel as the signal. so as long as you take in account the voltage drop you should be ok.

Thanks Tim for your replay.
I see your point with a problem on RX lines. Looks like more code will be required in any event. I think it will be an easy way out to just bring another RX line (RC5) for the 485 com, share the TX line, and write another routine for 485. A little more brainstorming is in order. Thanks again!

[Cobra_Phil]

Here is a good link describing the wiring schemes.
http://www.infocellar.com/networks/new-tech/PoE/PoE.htm