modbus tcp function block writes only when value changes?

Hello,

I´m currently working on a ModbusTCP connection to another computer.

A problem I found is that the function blocks seem to only write a value once when it has changed. They don´t write the same value again and again, which makes sense but I need it anyway (when the value is changed manually on the other computer I want to overwrite it automatically via Modbus). Is there a way to avoid/deactivate this behaviour?

Also I found that often the function blocks (read and write) need 3 loops or more to read/write the values. Is this normal or is there a way to optimise this? (IP is changed to 141.xx...)

Thanks and best regards!

Comments (10) New comment

by GustavA Rank: 61 on 4/4/2014 12:10:30 AM | Like (0) | Report

Are this Function block in AC500 or???

by Johanness Rank: 976 on 4/10/2014 2:05:36 AM | Like (1) | Report

Problem is solved, thanks! But it is AC700F...

by Sumit Gargav AKS expert

Rank: 3 on 4/10/2014 6:50:33 PM | Like (0) | Report

That's why very important to tag question with controller, control system while asking question or highlight that in question text.
Never mind, this was the case with MODS(slave) or MODM(Master) block ? in case of MODM blocks you can enable "Auto requests" via marking up check box in parameterisation. How you get resolved the problem ?

by Johanness Rank: 976 on 4/14/2014 7:37:33 AM | Like (0) | Report

Ok, sorry! I´ll tag the controller next time!
In my case it´s Modbus TCP Master. Right now I just call the function blocks multiple times to be sure everything worked but this is not really a solution.
Now I found out that when I use multiple function blocks (e.g. 3x read 8 registers) in a row and use the debugger, they do not read values in every cycle.
E.g. Block1 and 3 request the values in the first cycle (and receive them in the 2nd?!) and Block2 requests in cycle 2 (and receives the values not before cycle 3).

The problem with writing the same values again and again is "solved" by just calling the function block twice. First time with REQ=false, 2nd tim with REQ=true.

by jooseong10 Rank: 509 on 7/23/2014 8:48:08 AM | Like (0) | Report

Johanness,

I am using Freelance Control Builder F 2013. I am trying Test ModbusTCP connection to another computer too. I am having a lot trouble since this is a new software.

If you are using Freelance Control Builder F as well, would you please upload the example app?

Thanks.

by Johanness Rank: 976 on 7/24/2014 1:48:47 AM | Like (2) | Report

Hey,
yes I use CBF 2013. Can you tell what problems you have? The project got too complex and big to upload it.
But maybe I can pick out some pieces that will help you!
I got everything working like it should in the meantime.

by jooseong10 Rank: 509 on 7/24/2014 7:58:33 AM | Like (0) | Report

Allow me to explain my situation here. I am using CBF2013 with AC900FR.
I am trying to read the data from a SEL box (Schweitzer Engineering Laboratories).
The SEL box will be the master and the AC900F will be the slave. The starting address from the SEL box will be 400020[0] to 400020[15]. In another words, the address i am trying to read is from 400020 bit 0 to 400020 bit 15.

In my CBF, i have configured the hardware structure. The IP address for the AC900F is 172.0.0.1 and the IP address for SEL box is 172.0.0.10. I am using FBD, and i have choose MODS_R1C.

What is my start address in the "parameters:Read Coil 1 MODS_R1C" windows supposed to be?

by admin Rank: 29 on 7/24/2014 7:47:25 PM | Like (0) | Report

Dear J & J

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