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Altera_Forum
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12 years ago

Difference Between Reserving Unused Pins via Device Settings and Pin Planner

My device settings are such that all unused pins are reserved as "input tri-stated with weak pull-up."

With these settings, what's the difference between:

A ) assigning a pin with Pin Planner and simple leaving it out of the hdl, and

B ) marking it reserved as "input tri-stated" in Pin Planner

I ask because they sound like they should produce exactly the same result, however they don't. I get a different checksum on the programming files and when the probe the board, it seems like the pin is actually drawing current when I reserve it in Pin Planner.

What am I missing here?

4 Replies

  • Altera_Forum's avatar
    Altera_Forum
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    12 years ago

    what's the default for unused pins in your design? sounds like maybe it's Input Tri-Stated with Weak Pullup?

  • Altera_Forum's avatar
    Altera_Forum
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    12 years ago

    Yeah, unused pins are reserved as "input tri-stated with weak pull-up."

    When I assign signals to pins in Pin Planner and leave the signals out of the hdl, missing signal warnings are generated by the fitter, but the pins are in fact tri-stated. This is my first time using Altera and figured the preferred way of reserving pins is to mark them as reserved in Pin Planner rather than leaving their signals out of the hdl and letting them default to whatever the unused pins design setting is. However, reserving pins as "input tri-stated" in Pin Planner generates a different programming file and is electrically different than assigning a signal to a pin in Pin Planner, leaving the signal out of the hdl, and setting unused pins to "input tri-stated with weak pull-up" in design settings. This is what is confusing me.
  • Altera_Forum's avatar
    Altera_Forum
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    12 years ago

    i would expect different programming files based on whether the specific I/O is just tristated or is tristated with a weak pull up

    or have i missed something? :)
  • Altera_Forum's avatar
    Altera_Forum
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    12 years ago

    No no, I missed something. "input tri-stated with weak pull-up" isn't an option in Pin Planner, which I guess makes sense, so I assumed they had just shortened it to "input tri-stated."