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Altera_Forum's avatar
Altera_Forum
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14 years ago

Need a help on signalTap clock setting

Hello all,

I have to say sorry for making couple of questions in a short period.

By the way, I am trying to get familiar with SignalTap but I have somewhat weird wave on my screen.

I am using 100 MHz system clock. All data going in and going out are processed according to the system clock. To capture the data, I made 300 MHz clock for solely SignalTap. However, my screen shows the 100 MHz clock does not look like 100 MHz; Duty cycle should be 50% but it looks like 1/3.

I am appending a screen capture.

I am new to SignalTap, so any suggestion or comment would be much helpful and appreciated.

Thanks,

2 Replies

  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    14 years ago

    The acquisition clock is synchronizid to the 100 MHz clock, so one samples high and two low is just what you should expect. In addition, the sampled data will be wrong in part due to timing violations.

    There are only a few cases, where SignalTap acquisition with a clock rate higher than the system clock can be meaningful, e.g. when displaying asynchronous external signals. At worst case, it prevents timing closure of the design and can even cause timing problems in design parts, that are O.K. without SignalTap.
  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    14 years ago

    --- Quote Start ---

    The acquisition clock is synchronizid to the 100 MHz clock, so one samples high and two low is just what you should expect. In addition, the sampled data will be wrong in part due to timing violations.

    There are only a few cases, where SignalTap acquisition with a clock rate higher than the system clock can be meaningful, e.g. when displaying asynchronous external signals. At worst case, it prevents timing closure of the design and can even cause timing problems in design parts, that are O.K. without SignalTap.

    --- Quote End ---

    Understood. Thanks a lot!