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Altera_Forum's avatar
Altera_Forum
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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

I am sure those resistors are 1K. I've also tried 100ohms, but just to see if it changes something.

Thats my own PCB with EP3C40. Two boards are behaving the same, so I suppose the problem could be somewhere in the schematic. I've connected all VREF pins to 1.25V and all banks where memory is connected is powered 2.5V. The FPGA gets hot only when I upload a design which use memory controller. The PLLs are fine - separately works OK and using altmemddr works fine too.

Series termination: 22ohm, parallel termination 47ohm. I am not sure where else I could do a mistake.