input register is limited to 125

[TheRealRommel]

hey folks,

Im using a NI MODBUS.vi to read out my registers coming from a fieldbus over TCP. The Registers start at 0 and the last register will be something around 150.

Problem: the TCP register readout is limited to 125 registers. I guess it something to do with the 16bit version of my NI modbus.

Question: is there any possibility for me to read out more than 125 registers?

specs: labView 2013 pro develop

I would be happy to have some help on this one!

Cheers

[K C]

Hi,

As for as I know this is the 255 bytes ModBus limit. Reading Multiple registers the answer for 125 register is:

<slave add>, <command>, <# bytes>, <data>, <CRC> 

250 data byte + 5 bytes overhead = 255 bytes

Kees

[TheRealRommel]

Thanks for the fast answer!

I'm sorry to tell you that, but im quite new to this software. I don't get your answer 😕

What should I do with that commands you posted?

Cheers

PS: to be a bit more precise: I use the MB Ethernet Master Query read Input registers.vi

[K C]

Hi,

You mentioned software and LabVIEW, but you asked about ModBus.

ModBus is a communication protocol (not from NI). Within LabVIEW you can use this protocol.

The ModBus message length is maximal 255 bytes. If you want more data you have to use more than 1 command..

Kees

[TheRealRommel]

i cant find the command line do change anything. to make it a bit easier i wlil show you a picture of my structure.

http://imgur.com/bk4W0hd

With saying that i need one more command, do you mean i  have to double the Modbus VI in labView, to have enough bytes to read out more than 125 registers?

Cheers