Virtex 4 Config

Jun 13, 2007 4 Replies
M

Hi



Could someone just confirm for me that I can connect the config block t



3.3V in a Virtex 4 device. I have checked the data sheet and it seems t indicate this. I just want to check as I have been using Virtex 2 Pr devices which need to be 2.5V.

Jon


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D

Maxascent,

It is unclear on what you mean by powering the "configuration block" to

3.3V. You can power Vcco_0 (aka Vcco_config) to 3.3V. Be sure to read the V4 Configuration UG (see pg 15) on the requirements for all the dedicated configuration input pins and other requirements based on your configuration mode.
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-David

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M

Just had a look at some of the Xilinx development boards e.g. ML405 an they seem to have Vcco_0 connected to 3.3V but have the pullups on done init_b connected to 2.5V. Is it possible to have them pulled up to 3.3 instead? The documentation seems a bit vague about what supply you need t use.

Jon

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D

Jon,

I found where we have some info on mixed voltage environments in the config section of the Virtex-II UG

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(see pg 281) While this is not a V4 Users Guide and your issue is not specific to the JTAG pins, the information is applicable to your device. The main point to keep in mind is that the Vih-min for LVCMOS33 is 2.0V. At 2.5V on the pull-ups for DONE and INIT, you exceed this by ~500mV and are OK (assuming no SI issues in the PCB). This may explain the mixed voltages on the ML405.

If you have Vcco_0 at 3.3V the configuration pins are expecting LVCMOS33 levels, thus there is no problem with having the pull-up Vcc to DONE and INIT at 3.3V.

-David

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