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ADM3491 half mode configuration without using Enable Pins

Category: Hardware
Product Number: ADM3491


We are using ADM3491 RS422/485 transceiver for our application.

Can i short Driver and Receiver pin (A &Y,B&Z) also DE pin connect to 3.3V(Pull up) and RE# connect to Gnd(Pull down).

For half duplex operation can i use above configuration.


Arumuga Raj S

System Engineer

Thread Notes

Arumugam2608 - Moved from Power Management to Interface and Isolation. Post date updated from Tuesday, December 5, 2023 to Tuesday, December 5, 2023 to reflect the move.

  • Hi Arumuga,

    For half-duplex configuration, the connections A to Y and B to Z are correct. Setting DE to high (pull high to VCC) and /RE\ to low (pull down to GND) turn on both the driver and receiver the same time, signal passing from driver to the bus and looping from driver to receiver. So please be sure you can release the driver from the bus (DE = low) if you want the receiver be able to only follow from the bus.



  • Hi Jane,

    Thank you for your reply.

    In half duplex connection can i directly connect to the other driver output(driver to driver shorted),then what will happen

    Can i use series resistor for short circuit protection.


    Arumuga Raj S

  • Hi Arrmuga,

    The min. input resistance of the ADM3491 receiver is 12kohm. The ADM3491 allows up to 32 transceivers on the bus. It really depends on the load on the bus. In addition, a driver typically includes short-circuit protection. You can check on the Driver Short-Circuit Output Current spec on the datasheet.