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Altera_Forum's avatar
Altera_Forum
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11 years ago

cyclone 3 PLL[1..4]_CLKOUTp

Hello to all!

I'm reading the "Pin Connection Guidelines" for cyclone3 and cyclone4E.

In cyclone3 doc i read : "These pins can only use the differential I/O standard if it is being fed by a PLL output"

In cyclone4 doc i read: " Each pin can be assigned to single-ended or differential I/O standards if it is being fed by a PLL output"

I have a cyclone3 custom board, and i need to use a PLL output pin in a single-ended 3.3 LVTTL mode.

Can i do it?

Or i need to change my cyclone 3 to a cyclone4E?

4 Replies

  • Altera_Forum's avatar
    Altera_Forum
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    11 years ago

    Yes, you can use dedicated PLL outputs in single ended mode on a cyclone3. This is not inconsistent with the statement "These pins can only use the differential I/O standard if it is being fed by a PLL output".

  • Altera_Forum's avatar
    Altera_Forum
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    11 years ago

    Tnx gj_leeson.

    In cyclone 3 if i use a clkoutp in single ended, can i use the associated clkoutn for general pourpose I/O pin?
  • Altera_Forum's avatar
    Altera_Forum
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    11 years ago

    You will be able to use both clkoutp & clkoutn as independent general purpose, single ended I/O.

    Can I assume you want to drive clkoutp from the PLL?

    Yes, you should be able to both drive clkoutp (as a single ended signal) from the PLL and use clkoutn as a general purpose I/O pin.

    I've just tried this, successfully, albeit with a Cyclone IV part - I don't have Cyclone III installed. It will quite happily allow me to use clkoutn as an input or output signal whilst using clkoutp as a single ended PLL output signal.

    Put a small project together and let Quartus give you the answer for Cyclone III.

    Cheers,

    Alex
  • Altera_Forum's avatar
    Altera_Forum
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    11 years ago

    By the way, one quick way to find out if a pin assignment is valid or not is to use the pin assignment editor. It will tell you if you're doing something illegal.