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RS485 modbus communication-maximum number of nodes

Jayaram C B
Intellectual 370 points
Other Parts Discussed in Thread: ISO3086

Dear Sir,

We are planning to use ISO3086DW RS-485 TRANSCEIVER in one of our projects. This transceiver shall be in one of our electronic modules and there shall be 40 such modules in a typical application. We are planning to interface these 40 modules with a HMI(human machine interface) unit which would act as Modbus master. Is there any limitation that number of nodes shall be less than 32? Or can i interface these 40 modules with one HMI?

Thanks in advance for your reply.

 

Regards,

Jayaram C B

  • 0
    TI__Mastermind 21799 points

    Hi Jayaram,

    Sorry for the delay in no one getting back to you. In RS485 they specify the number of units allowed in a network in unit loads. They limit the number of "unit loads" on a single twisted pair bus to 32. This means that since the ISO3086 adds 1/8 unit load to the bus, you can have up to 8*32 nodes on the network (or 256 total nodes).

    Thanks,

    John