Cyclone3 external clamp diodes

[Altera_Forum]

I am getting the following warning and I have no idea why. Do I really need external clamp diodeas?  

 Warning: Following 17 pins must use external clamping diodes.  Info: Pin data[0] uses I/O standard 3.3-V LVTTL at B3 ....... etc

[Altera_Forum]

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:    --- Quote Start ---  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.  --- Quote End ---  

[Altera_Forum]

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

for a discussion on this topic.

[Altera_Forum]

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

[Altera_Forum]

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.

[Altera_Forum]

Fist ,Quartus must be set in the right condition. 

S,check your design.  Your design is the crucial point! Hope it can help you ！

[Altera_Forum]

Clamp diodes can be used to make a pin tolerant to higher input voltages than what they are specified to operate. For example, if you have a 3.3V LVTTL input buffer. And you want to make it 5V tolerant you can use an external clamp diode to clamp the voltage and limit the current to prevent damage and allow operation (Driven by 5V). Same notion applies for lower voltages.