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one wait singal using for multiple CS

Michi Yama
Guru 10030 points

Hi,

My customer would like to use one WAIT pin for multiple CS( Customer would like to use both asynchronous I/F and synchronous I/F  each CS with one WAIT pin).

I had asked this using is possible or not on E2E. And I got an answer "This is possible, but not advised." it is shown in the below site.

http://e2e.ti.com/support/dsp/davinci_digital_media_processors/f/716/p/187631/686695.aspx#686695

I would like to know the reason "This is possible, but not advised." Why is this way not advised?

Please let me know.

Best regards,

Michi

  • 0
    TI__Guru**** 170625 points

    hi Michi,

    Have you read section 11.2.4.12.2 NAND Device-Ready Pin from the AM387x TRM (sprugz7a.pdf)? There is some information inside.

    From my understanding, the usage of multiple CS to one WAIT pin is not advised, because the performance will suffer. I think that you can connect the CSs with wired OR on the WAIT pin, but there will be delays while switching from one CSs to other.

    I have contacted the SOC/pin-connection experts and asked this question. I will post their answer here once received.

    Best regards,

    Pavel




  • 0 in reply to Pavel Botev
    Guru 10030 points

    Pavel-san,

    Thank you for your reply.

    Your reply is helpful. But I need more information.

    1) You said " the usage of multiple CS to one WAIT pin is not advised ". I would like to know the nuance the meaning of "not advised".

    Is it cose to be bad(no guarantee)? or close to be not good?

    2) Please let me know  the meaning " performancee will suffer " in detail. For example,  it takes two more cycles, or it takes two times, and so on.

    I appreciate your quick reply.

    Best regards,

    Michi

     

  • 0 in reply to Michi Yama
    TI__Guru**** 170625 points

    Hi Michi,

    This is the answer from our GPMC IP design engineer:

    From a functional standpoint, you should be ok if you are using the wait signal for access monitoring for both CS. Is this what you are trying to do?
    Then, there is the electrical question. The devices you use should have open drain IOs for the WAIT signal for this configuration to be valid. If not, there will be contention on the bus, and functionality cannot be guaranteed.

    Best regards,
    Pavel