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Old December 6th, 2017, 02:47 PM   #1
cncsparky
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RL DataStation setup help

First Modbus project, rookie question I hope.

Modbus device -> DSPLE -> Control Logix L72 via Ethernet I/P

Need to read 5 Modbus registers. Four are 16 bit, one is 32 bit.

I have a block set up in the DSP with a size of 5 and mapped the appropriate Modbus registers.

My question is for the input instance of the Generic Ethernet module, what do I set the 32 bit size to?

I'm confused as to how the DSP moves the 16 bit words to the 32 bit tags. Will it only use two tags for the four 16 bit words, or will it use four tags and fill in the first 16 bits of the each tag? The 32 Modbus register I'm assuming will move to a single tag in the control logix.

Thanks!
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Old December 6th, 2017, 06:02 PM   #2
Bullzi
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Can you post your Crimson Code? Zip it first.

You will need 6 Gateway blocks reading 6 registers in the Modbus device. Modbus uses 16 bit registers max. So for floating point or long integers (32 bit) you have to read 2 16 bit registers and combine them in a Data Station Tag.

I am not sure how to answer your questions about a Generic Ethernet Module. Can you explain what module you are talking about? You shouldnt need anything more than a standard Ethernet Module to talk to the DSPLE and get your data.
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Old December 6th, 2017, 08:28 PM   #3
cncsparky
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The DSP is added to the 5000 project as a generic ethernet module. Data type is DINT, set an input and output instance, and a size. Does the 6 gateway blocks in the DSP = 6 DINTs in the logix project? Or would it be 3 DINTs?
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Old December 6th, 2017, 08:43 PM   #4
Bullzi
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I wouldn't add it as a generic module. I am not even sure if you can do that. Just give the DSP a IP that is in your control network. Then you set up the DSP to read the Modbus Registers you need and place that data into your PLC Tags. It is really pretty simple nothing special needs to be set up.

Here is a Youtube video that does a pretty good job explaining protocol conversion in the DSP https://www.youtube.com/watch?v=uLk5AdbPW2A

As for your question each Gateway Block will have only 16 bits of data (INT). So for each DINT you will need to read 2 consecutive registers. Same for a Real data type. So in your case with 4 INT's and 1 DINT you would need 6 Modbus Registers.

You can have the DSP write the INT data from the Modbus device to a DINT in the PLC if you want. I dont think it will affect anything. It will just write to the lower 16 bits of the 32 bit register.
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Old December 7th, 2017, 09:07 AM   #5
cncsparky
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Thanks. I think this answers my questions. One Modbus register = one logix tag. The input instance for my Ethernet module will have a size of 6, same as number of Modbus registers.

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Originally Posted by Bullzi View Post
As for your question each Gateway Block will have only 16 bits of data (INT). So for each DINT you will need to read 2 consecutive registers. Same for a Real data type. So in your case with 4 INT's and 1 DINT you would need 6 Modbus Registers.

You can have the DSP write the INT data from the Modbus device to a DINT in the PLC if you want. I dont think it will affect anything. It will just write to the lower 16 bits of the 32 bit register.
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