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Altera_Forum's avatar
Altera_Forum
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18 years ago

Cyclone 3 on-chip series termination (OCT)

Hi,

I am drawing schematics for a new system that uses a Cyclone 3 FPGA. I have some LVTTL (3V3) signals on which I would like to use a 50R series termination.

The Cyclone 3 has two possible 50R series terminations:

- not calibrated

- calibrated

The handbook doesn't specify the standards that can be used with the calibrated termination. Has anybody got this data?

The handbook mentions that the uncalibrated termination can be used with 3.0V LVTTL, it doesn't mention 3.3V LVTTL, is this a typo -or- is 3.3V LVTTL with on-chip termination not supported?

thanks and best regards,

Karel D

1 Reply

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

    --- Quote Start ---

    The handbook doesn't specify the standards that can be used with the calibrated termination.

    --- Quote End ---

    The standards for calibrated OCT are actually listed in table 7-3, the title has a typo. The 3.3V IO-standards don't support OCT due to restricted current strength allowance. The default 3.3-V LVTTL IO setting with current strength of 8 mA (see table 7-1) is near to the uncalibrated 50 ohm OCT setting that is used as default for other IO standards.