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Altera_Forum's avatar
Altera_Forum
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18 years ago

multi-Voltage I/O?

We need to connect 1V8 peripheral to FPGA,so i am not sure and clearly about the following problem :

if we wire ref-volt of the bank which I/O belongs to (VCCIO) into 2.5V, Can we make something in Quartus to force these output pins as 1.8V output when they are at high-level logic? I assigned these pins into 1V8 I/O standard, but their outputs are still 2.5V. Did we miss something here or if this can not solve our problem, so does Assigning these pins to 1.8V I/O standard in Quartus have any affection?

Thanks so much,

I hope to get your reply soon.

2 Replies

  • Altera_Forum's avatar
    Altera_Forum
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    18 years ago

    To my opinion, the device manuals are clear in this point. As they are rather verbose, you may have missed the respective statements. In my own words:

    - The output voltage of an I/O bank is exclusively determined by VCCIO.

    - VREF pins are used with special I/O standards as SSTL (with DDR-RAM). They only affect the behaviour of the inputs

    - assigning a different I/O voltage in Quartus only affects the current strength calculation and is used to check the pin assignment

    - interoperation of 1.8V and 2.5V devices may be possibly achieved with VCCIO of 1.8V, if VIH,min of the 2.5V devices can be kept. Otherwise you need a separate I/O bank or level translation.

    A poor mans level translation may be done by resistive dividers for unidirectional outputs
  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    18 years ago

    Thanks for your support, i am clearly now. I will use level translator for my problem.