How do I determine VREF pins for a specific device and package combination?
For example, in the Virtex-E pin-out table data sheet version 2.3 (http://support.xilinx.com/partinfo/ds022-4.pdf),a note regarding the pin-out for the FG680 on page 81 (Module 4 of 4) states:
1. VREF or I/O option only in the XCV1000E, 1600E, 2000E. (FG680 package!)
What is the pin when I have a V600E? Is it unused, I/O-only, or VREF-only?
(In the Spartan-IIE data sheet, this pins are listed per device/package combination.)
The bigger devices need more VREF, and the smaller ones need less. So by default, if it is not explained and the pin is designated <IO_VREF_#...>, then it is automatically I/O.
For example, examine pin AV14 in Bank 4, which is listed as IO_VREF_L144P_YY in the FG680 pin-out for "Note 1". In this case, the package file "v600Efg680.pkg" listed this I/O as "IO_L144_YY", which means it can be used as an I/O. The package file "v1000efg680" listed this I/O as "IO_VREF_4_L144P_YY", which means it can be used as either an I/O or a VREF.
The same applies to Spartan-IIE pin-outs. If it is NOT listed as "IO_VREF_#...", it is not a VREF in that package.
The best way to determine what pins are I/O is to view the package file for the specific device and package information. The package file can be obtained through one of the following methods:
1. Run "partgen -v <device_package_combination>" on a command prompt with the Xilinx software installed.
partgen -v v600efg680
The <device>.pkg file will be copied into your directory.
2. Access the package files on the web:
For Spartan-IIE, use the "partgen" command.