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SN65HVD78: Required enable/disable times, when both controlling inputs are connected

Part Number: SN65HVD78

Hi all,

in our design, both inputs /RE & DE are connected together, so that the device switches from receiver-enable directly to transmitter-enable – without a both-disabled state in-between.

Could you please tell us the required enable times for this case?

And what is the necessary minimum disable time, which leads to the long enabling time for the transmitter and receiver?

Currently, we just wait about 40 ns instead of 3…8 μs, and it works fine – but we aren’t sure if this is enough for ensuring stable operation under all circumstances.

Best regards,
Frank Brütting

  • Frank,

    In your application (connecting DE and REB together), you should not see 3 to 8us enable time. This long enable time only happens when both TX and RX are shut down and the device goes into low power mode. If DE and REB toggle the same time, either TX or RX keeps on. The device won't go into low power mode in all conditions. Please let me know if you have more questions about the enable time.