libmodbus

Access I/O on VME boards via Modbus/TCP

Asked by aladdinwu

I need to have remote Modbus/TCP access to the I/O signals on some VME boards. There is a RT Linux running on the board and I also tried to run a slave Modbus server in it - but I don't know how to make the Modbus server handle the real reading/writing of I/O to the VME boards.

Dose anyone have similar experience or any ideas on this issue?

Thanks a lot.

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aladdinwu (waladdin) said : 		#1

Or in other words, how can I define the mapping from modbus data model to the device application data (in my case it's VME boards), based on the libmodbus?

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Launchpad Janitor (janitor) said : 		#2

This question was expired because it remained in the 'Open' state without activity for the last 15 days.

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Stéphane Raimbault (sra) said : 		#3

It's up to you to map address Modbus do VME I/O, it's a just an arbitrary definition.
For pratical purposes, it's certainly easier to use continuous adresses, for example registers 0 to 10 to map 33 to 43 I/O of the VME board.

You must refer to the official documentation for more details, but coils are R/W bits, discrete inputs are RO bits, holding registers are RW 16 bits fields, input registers are RO 16 bits fields.

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aladdinwu (waladdin) said : 		#4

Thanks a lot, I have implemented it, basically the same as what you suggested. Thanks again!