Receiving error regarding MBAP Header Data

[tristansth]

I am having an issue trying to read data from a Wattmon EPM device,

I am able to manually poll it just fine using a modbus tester, but when trying to read from the scada I get this:

Request element group “Meter1”
Send (12): 05 A5 00 00 00 06 01 03 0B B9 00 02
Receive (7/7): A1 00 00 00 07 01 03
Error: invalid MBAP Header data

I verified with your Modbus Parser that both the tester and the scada are sending the same request (just with different identifiers)

—Modbus Tester Log—

Tx:000045-03 C7 00 00 00 06 01 03 0B B9 00 02
Rx:000046-03 C7 00 00 00 07 01 03 04 00 18 00 09
Tx:000047-03 C8 00 00 00 06 01 03 0B B9 00 02
Rx:000048-03 C8 00 00 00 07 01 03 04 00 18 00 09

——

Here are related screenshots:

https://drive.proton.me/urls/NB6YYG1HN4#753LiAQIXn0i

Any assistance would be greatly appreciated.

• This topic was modified 1 year, 1 month ago by Mikhail.

[manjey73]

Are you still polling this device in parallel with the Scada system?

[Mikhail]

Hi,
Could you share screenshots with Google Driver or https://imgbb.com/ ?
I can’t open proton.me
You can see that you receive other response using Modbus Tester. May be you should increase polling timeouts in Rapid SCADA.

[zzz]

I only saw gibberish when clients competing for RTU device or RTU over TCP or via TCP gateway.

In my recent S7-1200 case, the PLC with native TCP modbus simply ignores any latter clients, as long as the previous client doesn’t disconnect. (The programmer claimed that he has DISCONNECT bits set.)
And by ignoring, I mean, sometimes, it accepts connections, but hold up the connection till you quit, sometimes it simply reject any connection. 🙁
When this happens, since I can’t monitor his PLC’s eth port traffic, I can only tell him to restart his PLC, and it suddenly starts to work again.

[Author]

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