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Altera_Forum's avatar
Altera_Forum
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17 years ago

MAX II(EPM570) drive output

Hello,

My question is what is the maximum driver current of EPM570 device?

On our boards, we use EPM570 as an alternative of 74LCX16245/244 to buffer CPU data/address bus and drives devices on the other board, the two boards are connected by cable. The test result shows that the drive capability of EPM570 is kind-of weak because when we use longer cable, the boards does not work well, for shorter one, better. But for both cables, they work good when we use 74LCX16245/244 as the buffer.

So I am asking if we can modify some kind of settting from Quantus II to get the maximum drive output for EPM570?

Thanks and Regards,

Dennis

2 Replies

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

    FvM is absolutly right.

    You should measure your signal with a fast scope and correct setup (no GND clip thats a 1 wire loop antenna).

    have a look at the over and undershots of your signal. especially the undershots. they shift the gnd level down and some latches will get false levels for 1 and 0 recognition.

    with the current strength assignment you can adjust the over and undershots.
  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    17 years ago

    As you can see from the datasheet, MAX II supports output programmable drive strength, you can set it to maximum (16 mA for LVTTL) or minimum (8 mA). Maximum is set by default for all pins, if no additional Quartus settings are present. You can change the settings individually e.g. in Quartus Pin Planner.

    The question is however, if you actually verified the drive strength beeing too weak? It may be the opposite case of causing stronger reflections by a too high drive strength and/or faster edges. This can't be determined without real measurements, I fear.