rs485 4 wire (full duplex)

[FrankyCam]

This is a question about electronic more than labview properly, but i hope finding some answer.

I have a signal from a simulated encoder from a brushless motor driver. I want to acquire this by fpga module.

This signal have rs485 full duplex (4-wire) voltage level and my ni9401 has ttl level. I've a TTL/RS422 converter and a TTL/RS485 2 wire(half duplex) converter. what is the difference between rs485 4 wire and rs485 2 wire?

Thank you

[JÞB]

RS485 2 wire has a single TX and a single RX line where the voltages are compared to ground to determine if the data is a 1 or a 0.  RS485 4wire has TX+, TX- and RX+, RX- twisted pairs of wires that are driven with complementary voltages and the data value is determined by comparing the levels of the wire pairs.  4 wire offers a bit more noise immunity in most implementations

[RavensFan]

Jeff,

RS-232 has a single Tx wire and a single Rx wire where the voltage levels are compared to ground,

In RS-485 2-wire, there are only two wires (RxTx+ and RxTx-) that are differential to each other.  The same pair of wires handles receiving and transmitting allowing the pair of wires to be bidirectional.

[FrankyCam]

Exactly, Ravens fan.

In 2 wire (half-duplex) the transmitted/received switch is made by a RTS signal high/low. My doubts are in the case of rs485 full duplex. I found some wiring diagrams for TTL/RS485 4 wire (full duplex) converter, but it's the same that for TTL/RS422...but tension level are different...

[RavensFan]

"tension level" = ???

I have yet to figure out if there is any real difference between RS-422 and RS-485 4-wire.

I haven't seen anything related to an RTS signal in relation to either RS-422 or RS-485.

[FrankyCam]

Look at this link:

http://www.bb-elec.com/tech_articles/rs422_485_app_note/table_of_contents.asp

Thank you very much for your help

[FrankyCam]

In rs422  there's no RTS signal...and my doubt is that there's no difference between rs485 4 wire and rs 422 except for tension level

[RavensFan]

I still don't know what you mean by "tension level".  Are you possibly talking about voltage levels?  I'm assuming English is not your native language because you are using the phrase "I have a doubt" when you really mean "I have a question".

Looking at your link, (I've bought and used several isolators and converters from B&B Electronics), the only mention I see of RTS is related to the RS-232 protocol and how that signal wire is used to control the line state of the RS-485 side in an RS-232/RS-485/RS-422 convertor.

[FrankyCam]

Yes, 'voltage level'...excuse me.  English is not my native language...Doubt is correct, instead; maybe i've only tranlslated in English the phrase in my mind :). So thank you for the clarification about RTS

[JÞB]

---

@Ravens Fan wrote:

Jeff,

RS-232 has a single Tx wire and a single Rx wire where the voltage levels are compared to ground,

In RS-485 2-wire, there are only two wires (RxTx+ and RxTx-) that are differential to each other.  The same pair of wires handles receiving and transmitting allowing the pair of wires to be bidirectional.

---

That's what I get for posting from memory before coffee