Industrial Projects

RTU Modbus With CJ2M PLC and 3G3RX Drives on RS485

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Hi All, This is my first post so am sorry if anything is done incorrectly... I am having trouble with Modbus RTU on RS485 I have not worked with modbus before or Omron, So i am finding it hard to try and figure both out. The Hardware being used is: CJ2M PLC 3x 3G3RX Drives Is there a simple way of creating and sending the commands? ie a function block I have been looking around for a fb however i have had no luck with the ones i have found and i think it may be due to the RX Drives. Any help that can be provided will be much appreciated!
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Which port are you using to talk with the drives? Are you using the 9 pin Host Link port on the processor with an adapter, or are you using a CJ1W-SCU31 (or other SCU module)? There are protocol macros written to do Modbus RTU, it just so happens that I was testing one yesterday with a 3G3MX2 drive. So, if you are using the SCU module, I can provide some code to help.

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You seem to be a little green around the ears regarding Modbus etc, so may i suggest that you break the project down into small bits, understand those and implement and put together. Ie You know nothing about modbus.... there is a plethora of information on the web regarding the make up the protocol of modbus, have a read to understand what modbus is, what is a typical comm's frame in modbus, what is the CRC etc. This will give you good understanding of what to expect when debugging comm;s problems. Second, as the previous post explained, if you have a serial comm;s card (SCU....) then a modbus protocol macro can be used to simplify the modbus comm;s programming. Read about protocol macros, and how to use them. Third. To understand the comm;s first you can download a very useful tool called Multiway. This tool will allow you to connect from your PC to a drive talking modbus, as long as you have the wiring correct. BTW, you said that you have 3 x drives, so obviously you are using RS485 comm;s, arn;t you. Break the overall task into smaller tasks, then the problem aint that big

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Sleepy Wombat, I have read up on modbus and the command structure that is sent to the drives however have never got it to work. I will download and try Multiway and see if i can understand it better. Thanks to both for the replies and advice. Edited by Industrial Projects

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Does the cj2m not support easymodbus master as cp1 series does?

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Sorry! Easy Modbus Master is not supported on the CJ Series.

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Hi PMCR, I am using a CJ2M-CPU32 fitted with CP1W-C1F12 RS485 interface card, not SCU. Thanks anyway.

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Industrial Projects I understand what you have now. I would highly recommend adding an SCU module to the project if you are going to communicate Modbus RTU to the drives. You will save a great amount of time using the pre-written code to do the Modbus communications using the SCU module and the Protocol Macro that I have written for the SCU. PMCR

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PMCR Thank you for the code.. i am looking at doing that now as it will save so much time. Thank you for your help.

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Hi everybody,

I found this post searching for info about a similar problem I'm trying to solve.

I've been told than it's possible to communicate a CJ2M-CPU33 with this device through Modbus RTU using the built-in serial port of the PLC with a CP1W-CIF11 interface for RS422/485.

I only need to read some registers from the device to save them in the PLC memory, so it would be nice to avoid the expense of a SCU.

Do you know if this possible? Is there an existing FB useful for this?

Thank you very much for your help. 

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On 1/9/2017 at 7:46 PM, pedro_ant said:

Hi everybody,

I found this post searching for info about a similar problem I'm trying to solve.

I've been told than it's possible to communicate a CJ2M-CPU33 with this device through Modbus RTU using the built-in serial port of the PLC with a CP1W-CIF11 interface for RS422/485.

I only need to read some registers from the device to save them in the PLC memory, so it would be nice to avoid the expense of a SCU.

Do you know if this possible? Is there an existing FB useful for this?

Thank you very much for your help. 

Omron FB Library provide this _CPU012_SendCommand FB which can be used to send FINS-to-Modbus Command into the Serial Port, if it is configured as a Serial Gateway.

But you still need to manually create the Modbus data to be sent, and process the receiving

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Dear Sir

I have a CJ2M-CPU34 and CP1W-CIF11

so my question is as below:

1. could we use easy modbus way to connect CJ2M to other device through Modbus Protocol? if not we must use FB? and do you have any sample?

 

 

Best Regards

Mehdi

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On 8/19/2010 at 6:38 PM, Michael Walsh said:

Which port are you using to talk with the drives? Are you using the 9 pin Host Link port on the processor with an adapter, or are you using a CJ1W-SCU31 (or other SCU module)? There are protocol macros written to do Modbus RTU, it just so happens that I was testing one yesterday with a 3G3MX2 drive. So, if you are using the SCU module, I can provide some code to help.

Hello,

Can you send me the sample project for protocol macro and CX-Protocol.

I am using CJ2M-CPU35 and LS drives.

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