Cyclone3 external clamp diodes

In the Cyclone III device handbook, Volume 1, Section II, Chapter 7, Table 7-5 says, "The PCI-clamp diode needs to be enabled for 3.3-V/3.0-V LVTTL/LVCMOS." Table 7-8 says, "The PCI clamping diode must be enabled for input signals at 3.0 V or 3.3V."

If you do not have the built-in clamping diodes enabled, you have to provide them externally. There might be pins that don't have an internal diode available and so always require an external diode for these I/O standards.

I haven't looked at the app note, but the handbook also says this on page 7-14:

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For more information about Cyclone III PCI-clamp diode support, refer to AN 447: Interfacing Cyclone III Devices with 3.3/3.0/2.5-V LVTTL/LVCMOS I/O Systems.

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See AN 447 http://www.altera.com/literature/an/an447.pdf

for a discussion on this topic.

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There might be pins that don't have an internal diode available and so always require an external diode for these I/O standards.

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For some device families, internal PCI clamping diodes are available on only certain pins. For example, Stratix II has them only on column I/O pins. For Cyclone III, however, the device handbook on the page 7-14 I mentioned says, "Cyclone III devices provide an optional PCI-clamp diode enabled input and output for each I/O pin" (emphasis added).

Even though the internal diode is available on all Cyclone III I/O pins, you might not be able to use it. I have had to turn it off on dual-purpose pins being used for both user I/O and Active Serial configuration if I placed an input-only or bidirectional signal on those pins. Turning off the PCI clamping diode results in the warning in the original post for I/O standards that require inputs to be clamped.

After closely analyzing the pins Quartus was Warning me about, I have determined all these pins are the Active Parallel Dual Mode Pins- 47 Pins.

When I change the configuration mode, then I get 4 warnings.

Fist ,Quartus must be set in the right condition.

S,check your design.

Your design is the crucial point!

Hope it can help you ！