Forum Discussion

Altera_Forum's avatar
Altera_Forum
Icon for Honored Contributor rankHonored Contributor
10 years ago

MAX-V input impedance

Hi all,

I wander what is the IO and CLK input impedance of the MAX-V before first time programming the device?

(I don't want the CPLD to disturb the CPU signals that are connected to it).

Thanks,

Shony

2 Replies

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

    Hi,

    all Altera devices have weak pull-ups, which are enabled until the device enters user mode (i.e. during configuration, etc.). My understanding is that these are also applied while the CPLD is not programmed yet, at least I could not find anything contrary in the manuals.

    The spec for the MAX V is not as clear as e.g. for Cyclone devices, but as far as I understood it, the weak pull-up resistor depends on the applied I/O voltage, and it can be as low as 5 kOhm.

    So I'd say as long as all your CPU signals are properly driven (and you don't use any fancy open-emitter outputs), the CPLD should not interfere with the CPU.

    Best regards,

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

    --- Quote Start ---

    Hi,

    all Altera devices have weak pull-ups, which are enabled until the device enters user mode (i.e. during configuration, etc.). My understanding is that these are also applied while the CPLD is not programmed yet, at least I could not find anything contrary in the manuals.

    The spec for the MAX V is not as clear as e.g. for Cyclone devices, but as far as I understood it, the weak pull-up resistor depends on the applied I/O voltage, and it can be as low as 5 kOhm.

    So I'd say as long as all your CPU signals are properly driven (and you don't use any fancy open-emitter outputs), the CPLD should not interfere with the CPU.

    Best regards,

    GooGooCluster

    --- Quote End ---

    ----------------------------------------------

    Thank you GooGooCluster.

    Shony