Virtex 4 Config

Hi

Could someone just confirm for me that I can connect the config block to
3.3V in a Virtex 4 device. I have checked the data sheet and it seems to
indicate this. I just want to check as I have been using Virtex 2 Pro
devices which need to be 2.5V.

Jon

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.
http://direct.xilinx.com/bvdocs/userguides/ug071.pdf

-David


"maxascent" <maxascent@yahoo.co.uk> wrote in message 
news:vKednZYqqrRLZPLb4p2dnAA@giganews.com...
>
> Hi
>
> Could someone just confirm for me that I can connect the config block to
> 3.3V in a Virtex 4 device. I have checked the data sheet and it seems to
> indicate this. I just want to check as I have been using Virtex 2 Pro
> devices which need to be 2.5V.
>
> Jon 

Just had a look at some of the Xilinx development boards e.g. ML405 and
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 3.3V
instead? The documentation seems a bit vague about what supply you need to
use.

Jon 

Jon,

I found where we have some info on mixed voltage environments in the config 
section of the Virtex-II UG
http://direct.xilinx.com/bvdocs/userguides/ug002.pdf  (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


"maxascent" <maxascent@yahoo.co.uk> wrote in message 
news:urGdndaP-d9ZDO_b4p2dnA@giganews.com...
> Just had a look at some of the Xilinx development boards e.g. ML405 and
> 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 3.3V
> instead? The documentation seems a bit vague about what supply you need to
> use.
>
> Jon
>
> 

Thanks for clarifying this David

Jon