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Altera_Forum
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12 years ago

Potential Quartus Fitter Issue with Mixed Voltage Pins on Cyclone V

I am working on a Cyclone V design that is utilizing most of the pin resources. In my first pass, I let the fitter automatically assign pins. The issue that kept coming up is that, if not miti...
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Altera_Forum
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12 years ago

Hi RC.

Looking at your document, I agree with you. Looking at this table, it appears VCCIO of 2.5 support 3.0 volt inputs. They may have some floating reference voltage in the IO structure that allows this however.

Looking at the datasheet

http://www.altera.com/literature/hb/cyclone-v/cv_51002.pdf

Table 14 shows that for the 2.5V vccio it supports a VIH max of 3.6 V. This would allow 3.3 input operation. (with the recommended clamping diodes)

So my guess is the table 5-10 is in error, and they really support 3.3V inputs on a 2.5V bank. However, I would contact altera support to confirm this.

In either case, I would still recommend you separate the 3.3V bank form the 2.5V bank, just to avoid personal confusion going forward, unless you have ran out of IOs.

Pete