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AR# 12573

Virtex-II/Virtex-II Pro - DCI is not working as I expected. How do I debug this? (XCITE)


The I/Os I configure with DCI do not work as expected. How do I debug this?


To debug your setup, try the following suggestions:


- Use the most recent software version and service pack. The latest software update is available at:

Select the Updates and Service Packs tab.

VRN and VRP:

- Ensure that resistors are connected and are placed on the correct bank.

- VRN should be connected to VCCO (not VCC or VCCAUX).

- VRP should be connected to GND.

- On ES silicon, ALT_VRN/ALT_VRP pins (Banks 4 and 5) should not be used (refer to (Xilinx Answer 11208) for more information about using ALT_VRN/ALT_VRP vs. VRN/VRP).

- Compare a scope shot of your VRN/VRP waveforms to the example waveforms below (this will not be present if the bank is using only these outputs: HSTL_I_DCI, HSTL_3_DCI, SSTL2_I_DCI, SSTL3_I_DCI). Ensure that your waveforms have a similar shape. The absolute voltage levels and time scale are not important.

VRP/VRN scope shoot under normal operation
VRP/VRN scope shoot under normal operation

NOTE: VRP is the top waveform, and VRN is the bottom waveform.


- VRN and VRP must be connected during configuration.

- VCCO must be set correctly during configuration.

- Set the Match_cycle option in BitGen. The default value for this is "NoWait". If you use DCI, the value should be set to a specific startup cycle (0 - 6).

The Match_cycle option will stall the start-up sequence at the selected phase until the DCI match signals are asserted. If you would like to use a DONE pin as an indicator that DCI has found a match, set the value to a start-up cycle before the DONE_cycle setting (the DONE_cycle default is 4, hence this can be set to a cycle of 3 or earlier).


- In the ISE 5.1i design tools, the default setting for the Match_cycle option is "Auto". With this setting, Match_cycle will be automatically set to "NoWait" if DCI is not used in the design, or to "2" if DCI is used in the design.

- For information on BitGen options, please see:

1. Select the Design Tools tab.

2. Click on ISE Foundation/ISE WebPACK.

3. Select the latest release. A pdf containing all the software manual will open.

4. Select the Development System Reference Guide.

5. Select BitGen (Chapter 16 in ISE 10.1)

Next Steps:

If the above suggestions do not isolate the problem, please open a WebCase with Xilinx Customer Service at:


When you open your WebCase, please supply the following information:

1. The device and software version used.

2. The I/O standards used in the bank and whether they are used as input, output, or both.

3. A complete description of the issue(s).

AR# 12573
Date Created 08/29/2007
Last Updated 12/15/2012
Status Active
Type General Article