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SYosh17's avatar
SYosh17
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4 years ago

How to change "Latch Type" in Resource Property Editor

Hi all,

When I looked at the circuit I generated using the latch primitive in the Resource Property Editor, it consisted of LUTs instead of Programmable Registers, which I didn't expect. And the Latch Type was "latch".
However, even though I used the LUT primitive to connect the output of the LUT directly to one of the inputs and configured a latch, the Latch Type was "none".
Could you tell me what the conditions are for the Latch Type to be "latch"?

Since the latch primitive can be specified as the From/To Target of Report Timing, timing information can be obtained. I want to make my own latch with this feature.

I am using Cyclone IV GX and Quartus 18.1.

8 Replies

  • sstrell's avatar
    sstrell
    Icon for Super Contributor rankSuper Contributor
    4 years ago

    A latch by its definition is made of gates, not registers. Trying to get reliable timing from a latch is not really possible. Why don't you just use registers?

    • SYosh17's avatar
      SYosh17
      Icon for New Contributor rankNew Contributor
      4 years ago

      Thank you for your answer.

      I'm trying to configure an asynchronous circuit and the circuit doesn't have a global clock in my circuit, so I can't use registers.

  • ShengN_altera's avatar
    ShengN_altera
    Icon for Super Contributor rankSuper Contributor
    4 years ago

    Hi,


    Check this https://www.intel.com/content/www/us/en/docs/programmable/683082/22-2/inferring-latches-correctly.html

    Probably can help you.

    Note: In some cases, timing analysis does not completely model latch timing. As a best practice, avoid latches unless required by the design and you fully understand the impact.


    Best Regards,

    Sheng

    p/s: If any answer from community or Intel support are helpful, please feel free to mark as solution and give Kudos.


    • SYosh17's avatar
      SYosh17
      Icon for New Contributor rankNew Contributor
      4 years ago

      Thank you very much for your reply.

      The document helped me.

      I actually tried synthesizing the simple_latch in the document. This circuit was configured using two LUTs, one of which had a "Latch Type" of "latch". The Cyclone IV has 4-input LUTs, so I think this circuit can be configured with a single LUT. Why does this circuit consist of two LUTs? Is there any way to configure this circuit with single LUT?

  • ShengN_altera's avatar
    ShengN_altera
    Icon for Super Contributor rankSuper Contributor
    4 years ago

    Hi,


    Any further update or concern?

    Do you need any further help on this?


    Thanks,

    Best Regards,

    Sheng


  • ShengN_altera's avatar
    ShengN_altera
    Icon for Super Contributor rankSuper Contributor
    4 years ago

    Hi,


    Since there are no further feedback for this thread, I shall set this thread to close pending. If you still need further assistance, you are welcome reopen this thread within 20days or open a new thread, some one will be right with you.


    Thanks,

    Best Regards,

    Sheng