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VTScada Lite Mod bus TCP connection help

Just downloaded the software and thought I had an easy project to start with. Took awhile to grasp the Tag hierarchy but think I have it.
My problem is this: Trying to setup VT to read from a Modbus TCP slave. I have tested the slave communication with a small Modbus TCP app, running on the same PC as the VT app and it works fine.

The ModBus TCP communication parameters are:

Slave IP address – 192.168.1.247
Slave Listening Port - 502
Slave Unit ID – 100
Slave Data Type – 03 Holding Register
Slave Registry Address/DataType - 843/uint16

All I want to do is read information from the above connection information and display it with a gauge. Every attempt has resulted in an Error 257
Once I get one gauge working I can get on with the rest of the project.

Any help will be greatly appreciated.

Thanks,
Pat Davitt

Just downloaded the software and thought I had an easy project to start with. Took awhile to grasp the Tag hierarchy but think I have it. My problem is this: Trying to setup VT to read from a Modbus TCP slave. I have tested the slave communication with a small Modbus TCP app, running on the same PC as the VT app and it works fine. The ModBus TCP communication parameters are: Slave IP address – 192.168.1.247 Slave Listening Port - 502 Slave Unit ID – 100 Slave Data Type – 03 Holding Register Slave Registry Address/DataType - 843/uint16 All I want to do is read information from the above connection information and display it with a gauge. Every attempt has resulted in an Error 257 Once I get one gauge working I can get on with the rest of the project. Any help will be greatly appreciated. Thanks, Pat Davitt

On the options tab select Open Modbus TCP, at least that is what I usually forget to do when switching units from rs-485 to ethernet

On the options tab select Open Modbus TCP, at least that is what I usually forget to do when switching units from rs-485 to ethernet

Century Control Systems, Inc. www.centurycontrolsystems-inc.com

Yea, I got it working. Took me awhile to conceptually realize that the TCP in Modbus TCP is just the transport layer, its all serial behind that. That, and setting the registry addressing to be zero based, instead of one based. Was getting some "message CRC errors", but they seemed to have settled down. Is there a parameter I can use to tune that?

Thanks for your help.

Pat

Yea, I got it working. Took me awhile to conceptually realize that the TCP in Modbus TCP is just the transport layer, its all serial behind that. That, and setting the registry addressing to be zero based, instead of one based. Was getting some "message CRC errors", but they seemed to have settled down. Is there a parameter I can use to tune that? Thanks for your help. Pat

Mel,

The system is Cat5e, hardwire connected through an industrial switch. The CRC errors seem to have vanished on their own. (Growing Pains?)

Have another issue: When I create a Modbus TCP, Analog Status tag for an address in a particular slave with the following properties it kills the entire feed. Believe it's a problem in the datatype or scaling.

Address: 40821
Source Info:
Datatype: signed int(16)
Scale Factor: 1
Range: -32668 to 32668

I have successfully read from this register from both an app on my PC and an Modbus object on another PLC. When I cast it as a signed word on that PLC and then store it in a Modbus slave register, the VT tag reads it with no problem. For some reason I can't get the value directly from the source.

Thanks,
Pat

Mel, The system is Cat5e, hardwire connected through an industrial switch. The CRC errors seem to have vanished on their own. (Growing Pains?) Have another issue: When I create a Modbus TCP, Analog Status tag for an address in a particular slave with the following properties it kills the entire feed. Believe it's a problem in the datatype or scaling. Address: 40821 Source Info: Datatype: signed int(16) Scale Factor: 1 Range: -32668 to 32668 I have successfully read from this register from both an app on my PC and an Modbus object on another PLC. When I cast it as a signed word on that PLC and then store it in a Modbus slave register, the VT tag reads it with no problem. For some reason I can't get the value directly from the source. Thanks, Pat

Sorry for the delay in following up, can you explain a little more about the issue? What do you mean by "kills the entire feed"?

Sorry for the delay in following up, can you explain a little more about the issue? What do you mean by "kills the entire feed"?

Software Developer with Trihedral

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