NI Modbus Library

[RTSLVU]

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@LV_Pro wrote:

Sorry, the error I am getting is "Error 538182 "Modbus Error: Illegal Data Address"....My issue is trying to figure out what the new ones, Micro820, (apparently AB is/has phased out the MicroLogix 800 series) aren't happy with, what a valid address for it might be. 

The manufacturer should have provided a "Register Map" that lists the proper address(es) for the values you need to read/write and when reading registers how to scale the integer(s) to the proper numeric value. Without that you are kinda hooped.

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[BertMcMahan]

Are there any protections in place to prevent reading some addresses on your new system? Can you read ANY addresses? I'd try writing a program to scan them individually, one at a time, and see when/if it throws an error. Or, like someone else mentioned, get a general Modbus tool to make sure the thing will actually talk to you.

Also, I second the advice to sniff the packets. Use NI IO Trace if you can, or try HHD Device Monitoring Studio (if it's serial).

[StevenD]

As I recall, some devices will let you read any number of registers at once, but some will complain if you try to read more than what is specified as one entry.

IE if there are two floats at registers 20,21,22,23, some devices would let you read all 4 registers at once. But some will throw an error if you try to read more than 2 registers from each location.