Xilinx Constraints Guide

Chapter 4: Xilinx Constraints
DCI Cascade (DCI_CASCADE)
Architecture Support
Applicable Elements
Propagation Rules
In Virtex®-5 and Virtex-6 device families, IO banks that need DCI reference voltage
can be cascaded with other DCI IO banks. One set of VRN/VRP pins can be used to
provide reference voltage to several IO banks. This results in more usable pins and
in reduced power usage because fewer VR pins and DCI controllers are used. DCI
Cascade (DCI_CASCADE) identifies a DCI master bank and its corresponding slave
banks. There can be multiple instances of this constraint for a design in order to specify
multiple master-slave pairs. BitGen uses information from this constraint to program
DCI controllers for different banks and have them cascade up or down. The placer
also uses this information to determine whether VR pins in slave banks can be used
for other purposes.
Each instance of DCI_CASCADE must have one master bank and one or more slave
banks that can be entered as a space-separated list. The first value in the list is the master
bank and all subsequent values are slave banks that get DCI reference voltage from the
master bank. This restriction does not apply to Virtex-6 devices. Cascaded banks must
be in the same column (left, center or right) and must have the same VCCO setting. For
more information, see UCF and NCF Syntax below.
Applies to Virtex-5 and Virtex-6 devices only.
A DCI_CASCADE attribute on the top level design block.
Placed as an attribute on the CONFIG block, and propagated to the physical design
object.
Syntax Examples
The following examples show how to use this constraint with particular tools or
methods. If a tool or method is not listed, you cannot use this constraint with it.
UCF and NCF Syntax
CONFIG DCI_CASCADE = " ...";
where
• = [1...MAX_NUM_BANKS]
• = [1...MAX_NUM_BANKS]
• = [1...MAX_NUM_BANKS]
• All values in the list are legitimate IO banks in the Virtex-5 device.
• The master bank must have an IOB with an IO standard that requires DCI reference
voltage. This restriction does not apply to Virtex-6 devices.
• All slave banks must have the same VCCO setting as the master bank.
• If there are banks between the master and slave, they should be able to cascade in
the required direction.
Example
CONFIG DCI_CASCADE = "11 13 15 17";
Constraints Guide
92 www.xilinx.com UG625 (v. 13.2) July 6, 2011