Running RS-232 over a long length of twisted pair cable, should TX/gnd and RX/gnd be paired, or should TX/RX be paired and gnd left on its own?

 

It should TX/gnd and RX/gnd.

 

You can also get cable with shielded pairs with O.A. shielded cable.
Max.

 

It should TX/gnd and RX/gnd.

So, say, blue is TX and orange is RX. Just tie blue/white and orange/white together for ground?

Would it be different fro RS-485?

 

Yes, RS-485 is different.
A and B lines make up a twisted pair, plus a common ground.

 

Yes, RS-485 is different.
A and B lines make up a twisted pair, plus a common ground.

Oh, because RS-485 has two lines for TX (+/-) and two for RX? I'm thinking of DMX here.

(I've been wondering about those USB-to-RS485 adapters that only have screw terminals for two wires. I guess it leaves out the common ground??)

 

Oh, because RS-485 has two lines for TX (+/-) and two for RX? I'm thinking of DMX here.

(I've been wondering about those USB-to-RS485 adapters that only have screw terminals for two wires. I guess it leaves out the common ground??)

I am more familiar with half-duplex networks using RS-485.
TX and RX share the same pair of wire labeled A and B or D+ and D- (similar to USB).
There are only two wires plus GND. The two wires are twisted to make a pair of differential signalling.

 

(I've been wondering about those USB-to-RS485 adapters that only have screw terminals for two wires. I guess it leaves out the common ground??)

Yes, no common ground really needed to operate. (differential pair)
Max.

 

Yes, no common ground really needed to operate. (differential pair)
Max.

Ah. Maybe I'll try it then. Just two wires. (I guess I was wrong about the pairs in DMX. I'll have to find out what the 2nd pair of wires is used for. They're labeled optional.)

Anyway, looking at RS-485 is what made me question how to pair RS-232. I did decide to pair RS-232 TX/gnd and RX/gnd. Now it's good to know that that wasn't a mistake!

 

The common method of RS232 now because hardware handshake is not really used/needed is to use 3 wire cable, TX-RX-GND.
depends what 'Long Length' is.!
Max.

 

Running RS-232 over a long length of twisted pair cable, should TX/gnd and RX/gnd be paired, or should TX/RX be paired and gnd left on its own?

Used to be possible to get twisted pair flat cable. It was a popular choice for RS232 runs.

There is a standard specification for RS232 that recommends the maximum cable length.

 

depends what 'Long Length' is.!
Max.

Probably too long! I don't know the distance, but the cable is run like a bus to control LCD TV's. Probably way beyond spec. I think it mainly just transmits control codes occasionally. The thought of multiple TV's possibly transmitting back at the same time scares me. haha (It wasn't my idea to do this.)

 

Probably too long! I don't know the distance, but the cable is run like a bus to control LCD TV's. Probably way beyond spec.

Baud rate is usually tied to distance.
Max.

 

Baud rate is usually tied to distance.

For TV control is can be slow. Probably 9600 at the most.

I wonder if the twisted pair makes any difference at all, really.