Forum Discussion

Altera_Forum's avatar
Altera_Forum
Icon for Honored Contributor rankHonored Contributor
15 years ago

Cyclone III warning 16 pins must use external clamping diodes.

Hi,

I just started noticing this Quartus message. I am using a Numonyx/Intel P30 flash chip running 2.5V IO for both cyclone 3 and flash chip. I didn't add clamping diodes to my hw design. Its kind of annoying to find out now because I followed the data book diagram which does not show any external clamp diode. Is clamping diodes necessary for flash configuration programming even if both CIII and flash are using 2.5V IO?

Thanks for any help.

Warning: Following 16 pins must use external clamping diodes.

Info: Pin FLASH_DQ[0] uses I/O standard 2.5 V at N7

Info: Pin FLASH_DQ[1] uses I/O standard 2.5 V at F4

...

2 Replies

  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    14 years ago

    The answer is in AN447 and similar publications, Altera expects signal overshoots exceeding safe voltage limits if no clamp diodes are used. If this actually happens depends also on the trace lengths.