Forum Discussion

Altera_Forum's avatar
Altera_Forum
Icon for Honored Contributor rankHonored Contributor
15 years ago

Can VREF be other than VCCIO/2?

Must VREF be equal to 1/2*VCCIO, or can it be, say, 2/3*VCCIO? BTW, I'm using a Cyclone III M164 package. (very small physical board constraints) I'm trying to interface to a chip that has...
Altera_Forum's avatar
Altera_Forum
Icon for Honored Contributor rankHonored Contributor
15 years ago

When the FPGA isn't configured, the VREF pins are disabled with a weak pull-up, as any other I/O pin. That's why you are measuring a value different than expected. Do a new measurement with the FPGA properly configured.