How many devices can be connected to Modbus RTU?

1

Hello,

Can anyone help me?
How many devices can a T3000 controller connect with Modbus RTU, for each Main, Sub port. I usually use 1 T3-Nano to connecte with many T3-TB-11i devices. In case I need more than 128 Variables (T3-Nano), is there a way to do it? (firmware or INPUT/OUTPUT instead?)

Thanks!

2

Modbus address’s are one bye so in theory you can address up to 255 devices. It would impractical to have this many devices on a single twisted pair though, it would be difficult to troubleshoot and maintain. A more reasonable maximum is perhaps 30-40 devices.

The T3-nano supports 2 subnetworks, there’s no limitations with one or the other subnet. So whatever number you decide to string together, up to 255 x 2 would apply.

The number of variables will limit you if you are doing any massaging or converting the data on its way through the T3-nano. If you are just passing packets from the main to the RS485 sub then there’s no need to use local variables, the packets will route through transparently from Ethernet to RS485 and back.

You can use the inputs as vars, one client has been doing that. Havent heard of anyone using the outpus as vars but it should work, now that I think about it.

3

Thanks for your reply! I will try it with INPUT and OUTPUT.

4

INPUT and OUTPUT on T3-Nano, can be used. I’m not sure about its stability, but it worked.

5

There is no problem with stability. We’re working on dynamically assigning resources so you can use VARS only and get a lot more of those if you’re not using ins/outs, etc, should be done in a month.

6

Thanks for your great work!