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Altera_Forum's avatar
Altera_Forum
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16 years ago

Max 7000: Epm7064s-5

We've been using an EPM7064S-TC44-5 with an external 100MHz clock for a while but now we have a need to increase the clock speed for our device. From the datasheet, the 7064S-5 has a fmax of 250MHz and a fcnt of 175.4MHz...assuming I understand it correctly, the important max speed is 175.4MHz but you can supply it with up to a 250MHz clock and it'll just run at 175.4MHz. First off, is that assumption correct?

Second - any recommendations on a clock for this? (and where to buy it) Its important that it's a 5V clock also. I've been searching for a good clock solution and so far I'm not finding much.

Any thoughts would be very much appreciated.

Thanks!

5 Replies

  • Altera_Forum's avatar
    Altera_Forum
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    16 years ago

    --- Quote Start ---

    but you can supply it with up to a 250MHz clock and it'll just run at 175.4MHz. First off, is that assumption correct?

    --- Quote End ---

    Clearly wrong. Synchronous registers must be exptected to stop operation above max fcnt.
  • Altera_Forum's avatar
    Altera_Forum
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    16 years ago

    So what's the point of the fmax value given in the datasheet if you need to respect the 175MHz fcnt value instead?

  • Altera_Forum's avatar
    Altera_Forum
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    16 years ago

    I'm not completely sure

    - You can implement combinational logic at a higher frequency

    - A non-feedback register can possibly use a clock frequency up to fmax

    I don't think, that it makes much sense to push MAX7000S to the limits. You most likely won't find a 5V crystal

    oscillator above 125 or 133MHz and have to use an ECL or LVDS oscillator or a discrete solution with a level

    translator. Also the dynamic power dissipation is rather high for the 5V node. With recent CPLD, you can achieve

    fcnt of 200 to 300 MHz.
  • Altera_Forum's avatar
    Altera_Forum
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    16 years ago

    Yes, it's somewhat clearer than "highest frequency for pipelined data" in the datasheet.