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Altera_Forum's avatar
Altera_Forum
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16 years ago

Vi and VCCIO

hello,

I am just starting designs with Altera devices and I hope my question will be easy to answer.

1. VCCIO is just a supply power for input and output buffers of the device.

2. If I set VCCIO bank in Quartus = 2.5 V this means that I have to connect 2.5 supply voltage to the VCCIO pin of the appropriate bank.

3. This means that I can connect only 2.5 V operating device to the output pins to this bank.

Am I right?

4. But what about Vi - input volatage? For example, Can I connect a device with TTL 3.3 V outputs (means it drives 3.3 V to the FPGA input pins) to the 2.5V bank?

Thank you in advance.

7 Replies

  • Altera_Forum's avatar
    Altera_Forum
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    16 years ago

    --- Quote Start ---

    Can I connect a device with TTL 3.3 V outputs (means it drives 3.3 V to the FPGA input pins) to the 2.5V bank?

    --- Quote End ---

    Generally yes.

    For details, consult the respective FPGA Device Manual, particularly the Multi-IO voltage part.
  • Altera_Forum's avatar
    Altera_Forum
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    16 years ago

    In my case, I would like to have 3,3 V and 2,5 V IO pins.

    As I use the NEEK there are at all banks several pins that require 2,5 V. Unfortunately there are flash, ssram, sdram and lcd pins spread on all banks whichrequire these 2,5 V.

    As I read in your Multi-IO voltage part of the documents, the input pins might not be the problem but ...

    Am I right that it is not possible for me to use the output pins at 3,3 V? I just would like to have 2 pins driven at 3,3 V.

    Thank you in advance.
  • Altera_Forum's avatar
    Altera_Forum
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    16 years ago

    which pins exactly are you planning on driving at 3.3V. There is very little GPIO brought out of the NEEK board.

    Jake
  • Altera_Forum's avatar
    Altera_Forum
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    16 years ago

    A couple of weeks ago, I tried to find some GPIOs on the NEEK ...

    alteraforum --> /forum/showthread.php?t=19529

    (sorry I'm not allowed to post links yet :( please copy & paste to see the thread ... )

    I know, there is a new version (v2.0) of the neek available which has ~10 GPIOs but I'm wokring on the old one.

    As I could not find any pin without a resistor or capacity in series or parallel I decided to layout an own PCB. I now have a PCB in between the Starter Kit and the HSMC cable. That board works far better than expected.

    Now I have direct access to the pins:

    N15, N16, H16, H15, C1, C2, T16, R16, F18 (only input), F17 (only input) L3, L4

    I just found out, that it is not a real big problem not to have the 3,3 V. The background:

    I'm triing to realise an SPI communication to a microcontroller which runs at 3,3 V. Today I found out that with more that 2,0 V this microcontroller detects the signal as high. As I will not use this setup in critical environments my 2,5 V should be enough.

    Anyway, If you have an idea how to get the pins running at 3,3 V please tell me. Might be a better solution.

    Leo.
  • Altera_Forum's avatar
    Altera_Forum
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    16 years ago

    I would say leave it at 2.5V if the microcontroller accepts 2.0V as Vih. That's what I do in my designs.

    Since it's your own adapter board, if you decide you need 3.3V, I would add level translation.

    Jake