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Altera_Forum's avatar
Altera_Forum
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14 years ago

EP3C MSEL voltage

I noticed in another thread that the MSEL lines are supposed to be tied to VCCA or GND, regardless of whether the other config lines are pulled to VCCIO or not. I must have missed that, because I have a bunch of working boards with MSEL tied to VCCIO (3.3V) All of them are configured via AS, and have one MSEL line tied to 3.3V directly. Because I'm using a 3.3V flash, the status/control lines are also pulled high to 3.3V. (nSTATUS, CONF_DONE, and nCONFIG) I did route 2.5V for the JTAG port, though. The boards have worked fine for years, so I'm wondering what the consequences are for tying the lines to a higher voltage? Thanks!

2 Replies

  • Altera_Forum's avatar
    Altera_Forum
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    14 years ago

    The initial release of EP3C datasheet stated that MSEL must be hardwired to GND or VCCIO; later VCCIO was corrected with VCCA. Probably your boards were designed using the preliminary datasheet as a reference.

    Anyway, MSEL pins are powered from VCCINT but there is no specification about maximum voltage allowed. I don't believe the difference between VCCA and VCCIO itself matters. The problem could rather be the fact your supply rails set up at slight different times and you device gets the wrong MSEL configuration.

    In your situation I'd follow the simple basic rule: don't change anything if it works. :-)
  • Altera_Forum's avatar
    Altera_Forum
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    14 years ago

    Our boards are back-ends to analog sampling systems - so we only use linear regulators to avoid coupling switching noise into the power planes. I was just concerned that the pin could fail over time, causing a boot failure in the field. Some of our boards go into places where it's not always trivial to ship a replacement unit. Thanks for the heads up.