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THVD1424: Half-Duplex Operation

Ryan Smith
Prodigy 40 points
Part Number: THVD1424

When using the THVD1424 in Half-Duplex mode, are collisions on the Z/Y TX/RX pins controlled automatically internal to the IC, when I can just keep both the TX and RX enabled all the time? Or do I need to use SW control (on /RE and DE pins) to enable TX / disable RX when transmitting, and enable RX / disable TX when receiving?

  • 0
    Guru 273570 points

    You can leave the receiver enabled at all times. This implies that you see your own transmissions on the RX pin.

    You must not leave the driver enabled at all times; this would prevent other drivers on the bus from working.

  • 0
    TI__Mastermind 46537 points

    Hi Ryan,

    As Clemens mentioned - when in half duplex mode Z/Y act as both receiver and transmitter depending on enable states. 

    You can leave receiver enabled at all times since the receiver is high impedance (assumed to be 96k minimum input impedance)  - if your driver and receiver are active the receiver will pick up on the message that you transmitted. 

    However you cannot leave the driver on all the time as only 1 driver may be active on the differential bus at any given time or you will have data collisions.

    So yes there needs to be some higher level control protocol implemented to either avoid collisions completely or be able to detect and resolve them. The caveat here is that RS-485 does not define how you do this - nor does it really care since RS-485 only defines the physical layer so it really is up designer what would be easiest control scheme to implement in the system depending on higher level system needs. 

    Please let me know if you have any other questions!

    Best,

    Parker Dodson