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Difference between Unit Load and Total Number of Loads for a RS585 Transceiver

Siddharth Gupta84
Intellectual 450 points

Hi,

I am using SN65hvd as a RS485 transceiver.

What is the meaning of Unit Load, why is it specified? Why cant cant total number of slaves\receivers that can be connected be directly specified. What is the significance of Unit Load in such scenario?

Kindly clarify.

Thanking you,

Siddharth Gupta 

  • 0
    TI__Guru 62910 points
    Hi Siddarth,

    The number of receivers that can be supported can be directly specified, and this is generally what we do on newer revisions of datasheets. Using RS-485's "unit load" concept is just another way to specify the same thing. Both parameters would just be a function of the input leakage current of the receiver input pins.

    Here is a good description of the relationship between receiver input leakage currents, the RS-485 unit load, and the number of transceivers that can share a bus:

    e2e.ti.com/.../2575.the-unit-load-in-rs485

    Regards,
    Max