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SN65HVD82: MODBUS communication units

Lakshmy V
Prodigy 20 points
Part Number: SN65HVD82
Other Parts Discussed in Thread: SN75176A,

Hi,

We used SN75176A in our project for RS485 MODBUS communication. But when we test it on field, due to fail safe resistor presence the number of drivers/units that can be interfaced with the master-node reduced to 3. To increase the number of nodes {32 drivers(including one master} via MODBUS communication up to 1200m, we are looking for an alternative in SN65HVD82DR part.

Can anyone confirm if we use the alternate (P/N:SN65HVD82DR ) our above said requirement can be met or not.

Also please share the fail safe bias resistor value used in SN65HVD82DR for our theoretical calculation.

Regards,

Lakshmy V

  • 0
    TI__Mastermind 25705 points
    Lakshmy,

    Yes, SN65HVD82 would help here, because it has about 96kOhm input resistance that is much smaller than 12kOhm of SN75176A. You can use this app note (www.ti.com/.../slyt324.pdf) for a guidance. Basically the equivalent resistance of the bias network should match termination resistor and the voltage drop generate should be large enough to make the idle bus state determined. Please let me know if you have any further questions.

    Regards,
    Hao