Communicate PM573-ETH PLC with PSTX Softstarter over Modbus RS485

Hello, ABB

I'm having trouble communicating an ABB PSTX Softstarter to an ABB PM573-ETH PLC over Modbus RS485. To start, I'll a list of the hardware I'm using:

-ABB PM573-ETH PLC
-ABB TB511 Terminal Base (I've made sure it's not an outdated version)
-ABB PSTX85-600-70 Softstarter

Conections have been made in the following manner (image1):

I've not used 120 ohms end resistors due to not having them at hand at the moment. However, I'd think I don't need them since my wiring is less than 2 feet, baud rate is set to 9600, and I'm trying a simple master-slave arrangement.

On the software side I'm using Automation Builder v1.2 and CoDeSys v2.3.9.49

Here's what I've done in Automation Builder (image2)

And here's what I'm doing in CoDeSys (image3). For the moment, I only want to read registers. Later on, I'll want to write)

On the PLC's display I can see a dot flashing besides "COM1". I assume this means Modbus configuration is done well. But maybe I'm wrong.

On the Softstarter, I'm getting an error: P1E00. Which, according to manual, means Fieldbus communication failure. These are the settings of communication parameters on the PSTX:
12.01 = Modbus RTU slave
12.02 = Modbus RTU
12.03 = On
12.04 = 11
12.09 = 9600
12.10 = Even parity
12.11 = 1 Stop bit

All other parameters of this section haven't been modified. I should also mention that I only have energized the control of the PSTX, I have no 3-phase power connected to it, nor a motor. But I am not receiving any other error message besides the one mentioned before.

When doing a login on CoDeSys, I get a constant error on the COM_MOD_MAST block, "8211dec". Which, according the CoDeSys's help, is the timeout error. This makes sense, since I'm not getting any reading on the array of words I've assigned to the DATA input of the COM_MOD_MAST. The error I get on the PSTX confirms that there's something wrong on the Modbus network.

At the moment I have no idea of what I'm missing in the program's configuration, or if my mistake is somewhere else.

I know I've detailed a lot of information here but it's to make it easier anyone who can to help me out.

Thanks a lot in advance!

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daguilara9 Rank: 295

Asked 2 months ago

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Answers

Hi,
Looking on your connection diagram, I could recommend to try disconnecting of term. 1 and 4 from COM1 of PM573.
Actually these are pull-up/pull-down resistors. In case you use them, for sure you have to connect external 120 ohms term. resistor

Try to connect directly term. 2 (RxD/TxD-P) and 3 (Rxd/TxD-N) of COM1 to COM3 port of the softstarter. I'm not quite sure for term. 23 and 24 of COM3 of the softstarter, so you should try both variants:
2->23, 3->24
2->24, 3->23

For possible connections of COM1 port of PM573, you could look in Codesys help:

Serial interface COM1 of the Terminal Bases (PM57x, PM58x, PM59x), fig. 62 and 63

Comments (17) New comment

by daguilara9 Rank: 295 on 9/10/2018 2:09:45 PM | Like (0) | Report

Thanks, kstoilov.

I actually connected the pull-up/pull-down resistors since the connections indicated on CoDeSys for COM1 specify to use them. Here's what it says:

"If the RS-485 bus is used, each interconnected bus line (each bus segment) must be electrically terminated. The following is necessary:

-two resistors of 120 Ohms each at both line ends (to avoid signal reflections)

-in addition, a pull-up resistor at RxD/TxD-P and a pull-down resistor at RxD/TxD-N. These two resistors care for a defined high level on the bus, while -there is no data exchange.

It is useful, to activate both the pull-up and the pull-down resistors, which only are necessary once on every bus line, at the bus master. For this reason, these two resistors are already integrated within the COM1 interface of the AC500 Terminal Bases. They can be activated by connecting the terminals 1-2 and 3-4 of COM1."

I'll try without these resistors though and give you an update on it asap. I'll also try reversing the connections just in case.

Once again, thanks!

by daguilara9 Rank: 295 on 9/10/2018 2:42:24 PM | Like (0) | Report

UPDATE:

I removed the connections from pins 1 and 4. Nothing happened. Then I tried reversing the wires. Nothing still. I'm still getting a communication error on the softstarter and no memory readings on the PLC.

I think my connections are OK, where else could the problem be?

by kstoilov AKS expert

Rank: 7 on 9/10/2018 3:16:41 PM | Like (0) | Report

Hi,
For sure such resistors could be useful, if the producer invests installing them.
I just shared my own experience for one possible reason. I have such bad experience when once connected 1 and 4 (may be wrong ... :-)
You mentioned, that your line is with a very short distance and no termination resistors installed?
It would be nice to hear your feedback

by daguilara9 Rank: 295 on 9/10/2018 3:22:23 PM | Like (0) | Report

Yes. Right now I'm doing communication tests in my office so wire length is <2 feet. I don't think external resistors are required.

I removed the connections from 1 and 4, but I'm still getting the same problem.

Where you able to check what I have programmed? Maybe I'm missing something there.

Thanks a lot!

by kstoilov AKS expert

Rank: 7 on 9/10/2018 3:31:11 PM | Like (0) | Report

Hi,
Then may be you have to look in softstarter.
I'm little bit confused why it gives error message "Fieldbus communication failure" when it is slave.
May be because of 12.3=On ? The softstarter expects to receive some command from PLC, which you don't send?

by daguilara9 Rank: 295 on 9/10/2018 3:44:30 PM | Like (0) | Report

The softstarter can only act as a Modbus slave according to manual. Parameter 12.3 is "Fieldbus control", which, according to what I've read, should be turned to "On".

I followed the requirements, instructions, and memory mapping shown in this document:

https://library.e.abb.com/public/fb83d05d73254c8aa813385bcc6be6f5/1SFC132089M0201.pdf

To answer your last question. For the moment, I'm not trying to control de softstarter, but to only read its statuses. I don't know if only having the softstarter's control energized could cause the problem (I don't have any 3-phase or motor connected to it). Since the PLC is set as master, it should be interrogating the softstarter, or not?

by kstoilov AKS expert

Rank: 7 on 9/10/2018 3:45:49 PM | Like (0) | Report

Have you look in manual 1SFC132089M0201, page 6?
Reading of input registers require FCT=4 and start address 513 (which is 30513).
Try with set COM_MOD_MAST with:
FCT=4
ADDR=513
NB=1 or 2 (max. 11 registers are available in the softstarter)

by daguilara9 Rank: 295 on 9/10/2018 3:48:25 PM | Like (0) | Report

I'll try right now what you said in the last message.

by daguilara9 Rank: 295 on 9/10/2018 4:03:36 PM | Like (0) | Report

I tried it. Still no response.There doesn't seem to be any communication set between the devices.

by kstoilov AKS expert

Rank: 7 on 9/10/2018 4:13:31 PM | Like (0) | Report

Strange. Have you tried last advise with the other comments above (no 1 and 4, cross 2 and 3) ?
Then better try reading the softstarter with free ModScan?

by daguilara9 Rank: 295 on 9/10/2018 4:17:25 PM | Like (0) | Report

Yes, I removed 1 and 4 completely since the beginning. I haven't tried reading the softstarter with ModScan yet.

That means you don't find anything unusual on the Automation Builder / CoDeSys side? I'm using and ARRAY to read from the softstarter (as shown in the question's images), that shouldn't be any problem, right?

by daguilara9 Rank: 295 on 9/10/2018 4:18:39 PM | Like (0) | Report

What I meant was that on the DATA input of COM_MOD_MAST I have an ADR block and the variable feeding it is an ARRAY of words in this case.

by kstoilov AKS expert

Rank: 7 on 9/10/2018 11:28:56 PM | Like (0) | Report

ARRAY of Word is OK for ADR. Look for connection between nodes, -8211 means slave didn't respond to the master

by daguilara9 Rank: 295 on 9/11/2018 11:35:12 AM | Like (0) | Report

UPDATE (SOLVED):

While re-reading the manual, I found this:

"Note: If there is no message passed between the PSTX softstarter and the Modbus RTU master for more than 100ms, the PSTX softstarter will trip on
fieldbus communication failure protection (P1E00) and with the default configuration, the motor will be stopped. If the fieldbus communication system is setup in such a way that commands/requests are not continuously passed between the PLC and softstarter, this protection function should be disabled. The parameter 19.4 (Fieldbus failure op) can then be set to "Off"."

So I turned off this protection and I no longer got an error message on the softstarter. But, the ERRNO output of COM_MOD_MAST changed to "2". Which, according to manual is "COM_MOD_MAST: Error message from slave ILLEGAL DATA ADDRESS" By doing some tampering, I realized it was because I had set NB to 11 thinkng the softstarter started reading its analog input memory at 513. It turns out that by seting the ADDR input to 513, the softstarter will read from registers 514 to 523, thus, reading 11 registers caused the error. I changed NB to 10 and the problem was solved.

I am now getting readings on the 10 configurable AI of the softstarter on CoDeSys. There are some problems with scaling, so I will have to do some testing.

Thanks a lot, kstoliv. You sure helped me a lot! I'll let you know if I have any other problems. After this I'll try to control the softstarter via Modbus and later on I'll add an Emax breaker to the network. It should be interesting.

From this, I understand that the problem is in the ADDR input of the block; however, I'm writing exactly what the manual says me to write. Like the example you told me to try, my COM_MOD_MAST block is programmed like this:
COM=1
SLAVE=47 (I changed it too on the softstarter)
FCT=04
TIMEOUT=1000
ADDR=513
NB=11

by daguilara9 Rank: 295 on 9/11/2018 11:38:51 AM | Like (0) | Report

Please ignore the last part of my message. I had written that before and forgot to erase it.

P.S. In order to leave the protection at parameter 19.4 of the softstarter On without causing me any trouble, I changed the BLINK time to 50ms.

by kstoilov AKS expert

Rank: 7 on 9/11/2018 2:25:03 PM | Like (0) | Report

Hi daguilara,
Good to know your experience. It is interesting this softstarter "behavior".

by kstoilov AKS expert

Rank: 7 on 9/11/2018 2:28:37 PM | Like (0) | Report

Instead of blink at EN input of COM_MOD_MAST, there is a better solution - have a look in this post for example:
https://forum-controlsystems.abb.com/20199151/AC500-eco-Modbus-RTU-With-Automation-Builder-basic-License

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kstoilov

Rank: 7

Answered 2 months ago

Source: Codesys help COM1

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Communicate PM573-ETH PLC with PSTX Softstarter over Modbus RS485

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