adccommunitymod (AutomationDirect) asked a question.
Created Date: April 26,2004
Created By: jfenske
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I am new to the world of serial com work. The pinnouts of the DL06 Plc on port 2 for rs 485 include all of the adjoining signals for rs-485, 4 wire including the token ring signal leads. I understand the differental voltage concept of rs-485 but how does one go about using a 2 wire system on a comm system that is showing a tx for 2 wires and a rx on two other leads with a request to send send clear signal set. Is there anywhere I can get this information and the pinnouts on a dl06 port 2 for 2 wire rs-485 communication? Any help would be greatly appreciated. Jason Fenske. (Please excuse the poor spelling.)
Created Date: April 26,2004
Created by: Tom Jenkins
FOr two wire, simply tie the TX+ and RX+ together and hte TX- and RX- together.
Created Date: April 26,2004
Created by: Tech Guy
It can be found in the DL06 User manual in chapter 4. To save you a bit of head banging RS-485 only works with MODBUS. The user manual can be found here: http://www.automationdirect.com/static/manuals/d006userm/d006userm.html
Created Date: April 27,2004
Created by: Tom Jenkins
Techguy, you said "To save you a bit of head banging RS-485 only works with MODBUS. "
I'm afraid I don't understand this at all. Are you saying that on the DL-06 only Modbus communications commands access the RS-485 pins on the second comm port? I'm skeptical, but I'm willing to be proven wrong.
Or, are you saying that only Modbus communications protocol can be transmitted on RS-485 serial links? That I know for a fact is wrong, and I have personally used RS-485 for a wide variety of communications protocols from a wide variety of devices.
Could you please clarify?
Created Date: April 27,2004
Created by: Tech Guy
I'm afraid I don't understand this at all. Are you saying that on the DL-06 only Modbus communications commands access the RS-485 pins on the second comm port? I'm skeptical, but I'm willing to be proven wrong.
No sir. All protocols can access the RS-485 pins. After all they are the same pins that do RS-422. See below for the total answer.
Or, are you saying that only Modbus communications protocol can be transmitted on RS-485 serial links? That I know for a fact is wrong, and I have personally used RS-485 for a wide variety of communications protocols from a wide variety of devices.
This is not quite what I am saying. Generic RS-485 can be used with any communications protocol.
BUT... The RS-485 connection on the DL06 can only be used with MODBUS. It has to do with the reflection characteristics of RS-485 and the way the DL06 firmware has to deal with it. Yes, the termination resistors help, but apparently there is a bit more to it than that. (At least this is the way I understand it. If you need more clarification than that I will have to go get a Koyo engineer to explain why.)
I have done quite a bit of testing and talked to enough customers to believe that a few people who really understand RS-485 networking MIGHT get it to work with a protocol other than MODBUS, but the average technician will have an EXTREMELY difficult time getting it to work with any other protocol.
Created Date: April 28,2004
Created by: Tom Jenkins
Ok, then as I understand it, you are saying the RS-485 signals on the DL-06 port 2 pins are "off spec " a little bit. Does that apply at any baud rate, or only at the higher baud rates?
Does that mean that if I want to network several DL-06 units using DirectNet protocol I have to use RS232 to 485 adapters the way I did from the DL-240 port? What if I want to tie an operator interface with an RS485 port to the RS485 pins on the DL-06 one to one and not networked to any other devices - will this be OK using DirectNet or K-Sequence?
Created Date: April 28,2004
Created by: Tech Guy
What I am saying is that Koyo seemingly designed the RS-485 echo supression to work with MODBUS only. I personally really don't understand exactly why it doesn't seem to work with DirectNet or K-Seq. I have tried it myself and failed and have had enough customers try and fail that I recommend using MODBUS only.
Again, you might try it and succeed Tom. You are fairly experienced with our equipment and communications, so you may have better luck. But, I still recommend not to count on it, personally.
Created Date: April 28,2004
Created by: Tom Jenkins
Thanks. The reason I'm so interested is that I'm currently designing a system with a 250 master and four '06 slaves, each with an EZTouch O/I. I will take a look at options, but I may just use the 232 pins on the '06 and the 232/485 converters we 've used in the past with 250's and '05's. Of course, I may also just go to Modbus RTU protocol instead.
Created Date: April 29,2004
Created by: jackson
If you are using a 250 master and four 06 slaves, why not just RS422 (4 wire)? It is available in both of those CPUs.
Created Date: April 30,2004
Created by: Tom Jenkins
That was my intent, Jackson. However, I interpreted TechGuy's post to indicate that the problem was not restricted to 2-wire RS-485, but also 4-wire. TechGuy, is this correct?
Created Date: April 30,2004
Created by: Tech Guy
I have never had a problem with any protocol (K-Seq-, DirectNet, MODBUS) over a standard that uses 4 wires. It is just 2 wire RS-485 that is apparently limited to MODBUS protocol.
Again this is what I personally have tested and observed. Your milage may vary.