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SN74ALVC164245: Avoidance of bus contention issues with memory

Martin Grimmer
Prodigy 470 points
Part Number: SN74ALVC164245

Hello,

we have to guarantee, that there are no bus contention issues between memory and SN74ALVC164245.

What if it would be guaranteed to set DIR pin correctly, before we activate the level shifter via EN (approx. >=1ns setup time)? And for the disable, at first we deactivate the level shifter and afterwards set the direction back (approx. >=1ns hold time).

According to datasheet for such sequence the level shifter should change from "isolation state" to "B to A operation".

Is it guaranteed, that with this sequence the level shifter doesn't drives the wrong direction ("A to B operation") at no time?

Or could the case happen, that DIR pin sets the direction slower than the EN pin activates the shifter? If this could happen, which setup/hold time is needed to avoid contention issues?

Thanks & Regards
Martin

  • 0
    Guru 243120 points

    The purpose of the OE inputs is to avoid these problems; as long as you observe the switching times (ten, tdis), nothing wrong will show up on the outputs.
    (Apparently, there are no switching characteristics for the direction inputs; assume they are as slow as the OEs.)

    However, there is no guarantee that all pins have exactly the same speed. But I've heard rumors that the propagation skew is less than 1 ns.

  • 0 in reply to Clemens Ladisch
    TI__Intellectual 2100 points

    Clemens Ladisch said:

    The purpose of the OE inputs is to avoid these problems; as long as you observe the switching times (ten, tdis), nothing wrong will show up on the outputs.
    (Apparently, there are no switching characteristics for the direction inputs; assume they are as slow as the OEs.)

    However, there is no guarantee that all pins have exactly the same speed. But I've heard rumors that the propagation skew is less than 1 ns.

    Hey Martin, 

    I would recommend taking a look at Clemens' answer since he has supplied you with a good one.

    If this answered your question please hit the green verification button below so others can find this solution more quickly! If you have additional questions send them along and we'll work to answer them as quickly as possible.

    Best Regards, 

    Nick