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HAlex's avatar
HAlex
Icon for Occasional Contributor rankOccasional Contributor
4 years ago
Solved

Cyclone IV JTAG pins connected to VCCA (2.5V) with IO bank of 3.3V

Hello I am using Cyclone IV GX (EP4CGX150CF23C8N). JTAG and configuration device (AS - EPCQ128ASI16N) connection done as described on figure 8-29 (page 220 of Cyclone IV device handbook Volume 1...
  • ak6dn's avatar
    ak6dn
    4 years ago

    For 3.3V LVTTL, the spec for VIH(min) is 1.7V and VIH(max) is 3.6V. So a pullup to a voltage between these limits (2.5V) is OK.

    Normally tho one would connect the pullup to the same voltage source as drives the VCCIO for those I/O pins.

    The only concern would be what are the powerup characteristics of the 2.5V and 3.3V rails in your system?

    Do they powerup simultaneously, or is there a significant time differential in their ramp rates?

    For example, if the 2.5V rail turns on significantly later, you could get into the situation where the pullup to 2.5V is actually a pulldown.

    Personally I would connect the pullups to the same voltage source that drives the VCCIO pin for those I/Os.

HAlex's avatar
HAlex
Icon for Occasional Contributor rankOccasional Contributor
4 years ago

Hello

My 2.5V turns ON after 3.3V (DC-DC regulation from 3.3V to 2.5V) with S.S setup of few mSec (less than 5mSec).

Standard POR time in Cyclone is up to 50mSec - so it should be ok.

But just to be on the safe side I decided to do also an alternative connection for VCCIO (of 3.3V - Bank 9).

By default I will assembly resistors only to VCCA (2.5V).

Thank you very much

Alex