Modbus address

[ASTDan]

Hello,

I am using NI's Modbus library and have run into the folowing problem.  When I use the Master Serial query I want to read address 404198 however the input to the addres is 16 bit.

Any sugestions?

[Pnt]

You will have to modify the code of the sub-vi to accept bigger values.

Allthough check your hardware. You should be able to change it's address in a more logical value.

I have never heard someone using so big addresses (what is the point of this?)

[ASTDan]

The point is I am trying to comunicate with an Eaton Logic controller.  My customer has programed the PLC and has told me the data I need is at the above modbus address.

Thanks

Dan

[RavensFan]

Did you try just 4198?  The initial 4 of the 40,000 or 400,000 is usually implied.

[ASTDan]

I get a response, but I don't think it is the right data.

[RavensFan]

The other thing to check is that I believe there is an offset of one on the address.  So if you want 40001, you would put in 0 as your starting address.  So try 4197.

Also, I believe function code 3 gets the 40,000 series registers  which are holding registers.  Function code 4 is for reading the 30,000 series which are input registers.

[Pnt]

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ASTDan wrote:
I get a response, but I don't think it is the right data.

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If the address is not correct, it should not reply at all !

[ASTDan]

I think I was getting data from registers I am not interested in.

Anyway I bit the bullet and am in the process of making my own driver.  I was able to sucessfully comunicate via hyperterminal.  Now it is just a matter of coding it up.

Thanks!

Dan