Modbus Slave I/O Server 32 port limitation

[picky33]

i'm currently working on configuring a Modbus Slave I/O server and i can only view the first 32 comms ports. i currently have 108 serial ports installed on my chassis and i need to be able to communicate with all of them. Does anyone know how to get around this limit?

[billko]

I think depending on your OS, it could be a limitation of either Windows, LabVIEW or both.  Either/or, I don't think you can get around the limitation.

Oops I noticed only 32 ports.  What I said applies to a higher number of ports.  Sorry!

https://knowledge.ni.com/KnowledgeArticleDetails?id=kA00Z000000PAhzSAG&l=en-US

[picky33]

i'm running windows 10 and LabView2018 SP1. 

[Jacobson-ni]

Do you have to use the I/O server? Could you instead use one of the available Modbus APIs like https://github.com/NISystemsEngineering/LabVIEW-Modbus-API.

[picky33]

This is what i'm currently using. it has a limitation of only 1 Slave ID per Comm port and i need to be able to simulate multple slave ID's over 1 comm port.

I'm using ni modbus library 1.2.1.42 currently, if the software you mention above is not the same, let me know and i'll try it. either way i need to be able to simulate slave ID's on over a single serial port

[Kemens]

Do you have to use all the slaves simultaneously or is it okay if you connect with only one slave at a time?

[K C]

Hi,

Without knowing how your configuration looks like, I would use a I/O server from Moxa. You can connect to it through Ethernet and access all port with a different ModBus slave address.

Even better would be a RS-485 connection where you could connect aal slave to one wire.

Kees

[picky33]

Unfortunally all of them have to be used simultaneously. i have to simulate an entire process, this could mean controlling the pump which in turn causes me to control a valve and an A/C plant and a Generator and a motor controller, all for transfering fuel from one tank to another.

[picky33]

If you look at the picture below, my setup is as follows. PLC's are my masters there are 30+ with 4 RS-485 serial channels a piece so 120+ serial channels that i need to respond to. i'm using labview to simulate the pieces of equipment, Acting as Modbus Slave devices. i wrote slave id's up there to demonstrate that many of the PLC's respond to the same slave id's for different pieces of equipment. I can't change how the PLC's work or how they are configured, i can only change things on my end. Each comms channel may have 30-40 different slave ID's for different pieces of equipment and thats where the MODBUS I/O server is nice but it gets around this limitation, but i need the program to allow me to select comms ports higher then 32 to talk with all the PLC's.

[JÞB]

I would have to do some digging but, there are 2 different limitations that you have. 

1. Modbus addresses have bus Limits of 32 devices of which only 1 is the master

2. For multiple busses you need the master vis to be reenterant so they don't share dataspace.

Again,  I am not sure if that library is reenterant! But, the dialog shown in your picture looks like it does not expect multiple modbus masters.  Not surprising! Having 124 plcs in one system sounds unique. 

There are some 3rd party modbus libraries out there that may be worth looking into.