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SN65HVD75: Transmit-Driver and Receiver enable times 3uSec and above under what conditions.

Scott Morrill
Prodigy 60 points
Part Number: SN65HVD75

I'm using the SN65HVD75 with the REnot and DE tied together.  In the specification it claims that Transmitter takes 3usec typical to enable if receiver had been disabled, otherwise it only takes 10nSec typically.  I don't understand the reference to Receiver enabled or disabled.  SO like I've said I tie the REnot and DE together so I suppose the receiver is momentarily disabled.  In my situation do I need worry about the 3-7uSec Driver enable times tpzh and tpzl?

Likewise for the "Receiver enable time" do I need to worry about the 3 to 8uSec specifications when tying REnot and DE together.

Under what conditions do the longer enable times for the receiver or transmit driver come into play?

  • 0
    TI__Guru 62910 points

    Hi Scott,

    The reason behind the different specifications is that when both the transmitter and receiver are disabled, the device enters a low-power mode that shuts off much of the internal circuitry.  Waking up from that state can take a little extra time because those circuits need to be powered back up and settle to their nominal operating states.  When only one half of the chip is shut down, though, any shared/"global" circuitry is kept active so that transitions between transmit and receive mode can happen very quickly.

    Entering the shutdown mode requires the /RE be high and DE be low for some time.  I don't have the duration off hand unfortunately, but it is long enough that whenever /RE and DE are controlled by a common line you will never enter the shutdown mode.  So, the faster set of timing specs would apply to your application.

    Please let me know if this isn't clear or if you have further questions.

    Regards,
    Max

  • 0 in reply to Max Robertson
    Prodigy 60 points

    Thanks, Max.

    I thought that is what is was, couldn't make the connection to low power mode and just a disabled tristate drive situation, it wasn't clear to me for some reason.