Altera Cyclone 3 external clamping diode


During implementation I get the following fitter warning: Warning: Following 1 pins must use external clamping diodes. Info: Pin Nios2Processor:\b_uP_MemInt_I2C:i_Nios2Processor| epcs_controller:the_epcs_controller| tornado_epcs_controller_atom:the_tornado_epcs_controller_atom| the_tornado_spiblock~ALTERA_DATA0 uses I/O standard 2.5 V at N7

My design uses an EPCS flash (powered @ 3V3) and it uses pin N7, which is situated in a 3.3V bank.

This is confusing:

- The handbook uses a clamping diode to Vccio, in my case that is 3.3V

- Quartus tells me to add a clamping diode, it doesn't specify to which voltage but I guess that it is the 2V5

- Is the input buffer for the data0 pin powered by Vccio (3V3) or by Vcca (2V5) ?

Can you clarify this?

thanks and best regards, Karel D

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