Forum Discussion
Occasional ContributorCyclone IV JTAG pins connected to VCCA (2.5V) with IO bank of 3.3V
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.
Regular ContributorFor 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.
