DCI question

Hi all,

I have a very peculiar problem with some digitally controlled impedance (DCI) inputs on a Virtex2 device: whenever I enable the DCI on the inputs the signal levels go way down, without DCI I see about 800 mV and with the DCI on about 200 mV. The IO standard is HSTL_I_18, this is a QDR Sram interface design. Another strange thing is that I only see this behavior on the XC2V8000 device, the XC2V4000 and XC2V6000 devices work fine on the same hardware!? Any suggestions? Thanks,

--
jakab
Reply to
jakab.tanko
Loading thread data ...

Jakab,

Check that the Vrp and Vrn reference resistors go to the right supply. A common mistake is to have the Vrp (pmos) resistor go to Vcco (wrong), instead of ground (right), and similar for the Vrn resistor which should go to Vcco (right), not ground (wrong)

Be sure to actually measure the reference resistor value. Really tiny surface mount resistors are easy to get wrong: instead of 51 ohms, they may have placed 510 ohm resistors there! Seeing the markings requires a loupe or magnifying glass!

Also check you have used the right Vrp and Vrn pins for that bank. I know that some devices have alternate Vrn, Vrp pins, which require that the software know which ones you are using. I do not think this affects the 2V8000 (only smaller parts in smaller packages).

All the devices share the exact same cell for the DCI (layout), so there is nothing magic about the 2V8000.

Aust> Hi all,

Reply to
Austin Lesea

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.