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Altera_Forum's avatar
Altera_Forum
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14 years ago

5V i/O

Hello,

I need to have TTL (+5V for HIGH) inputs and outputs from an Altera DE0 board. Is there any easy way to configure it for I/O pins to operate at 5V?

Due to time constraint, I am trying hard to avoid making a board with voltage translators now!

Any suggestions?

Thanks

3 Replies

  • Altera_Forum's avatar
    Altera_Forum
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    14 years ago

    I myself using DE0 with 5V ICs. You can send a 3.3V LVTTL signal to a 5V TTL, that's ok. But for taking 5V signals as an input I use a serial 330 ohm resistor to restrict current and a parallel 3.3V zener diode before FPGA input. Works satisfactory for me for low frequency applications.

  • Altera_Forum's avatar
    Altera_Forum
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    14 years ago

    According to TTL specification, 3.3V level is sufficient, because TTL Vih,min is 2.0 V. If you want to drive 5V CMOS with Vih,min of 3.5V, a level translator can't be avoided.

  • Altera_Forum's avatar
    Altera_Forum
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    14 years ago

    Hi,

    on DE0_v.1.1_CDROM\DE0_CD-ROM_v.1.1\Schematic\DE0_V12_RELEASE.pdf page 17, all the VCCIO are connected to VCC3p3.

    The VCC3p3 comes from the REG3 on page 18 specific for 3.3V only, plus the VCCIO has a maximum rating of 3.9V (cycloneIII device datasheet P1) plus VIH max is VCCIO+0.3V.

    So I guess that you do need voltage translation.

    Regards.