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AR# 11004

Virtex Configuration - When the Startup_wait DLL option is used, the part does not configure (the DONE pin stays low)

Description

My design is targeted to a Virtex/Virtex-E device. I am attempting to delay startup until the DLL locks, using the Startup_wait property on the DLL.

However, this property is not allowing my device to configure. If I remove this property, my device configures correctly; however, if I use it, the device does not configure.

Solution

For a 1x clock:

This is a working start-up cycle configuration:

GTS_cycle: 1

GSR_cycle: 1

LCK_cycle: 2

DONE_cycle: 4

It is important to release GSR before the LCK_cycle. It is also important to release GTS before the LCK_cycle if external feedback is used. Failing to do so will keep the DLL from locking because the pin driving the external feedback clock will remain tri-stated and the DLL will never see the feedback clock.

To set the start-up options, edit the "bitgen.ut" file or set the options in the Project Navigator GUI.

In the Project Navigator GUI:

1. Right-click "Generate Programming File" -> Select "Properties."

2. Under the "Startup Options" tab:

Enable Outputs = GTS_cycle (C1)

Release GSR = GSR_cycle (C1)

Release DLL = LCK_cycle (C2)

Done = DONE_cycle (C4)

NOTE: Setting the GTS and GSR cycles before the DONE cycle might cause problems in daisy-chain applications.

For a 4x clock:

For the 4x clock, logic using the SRL16s is needed to implement it, so the GWE (global write enable) must be set before the LCK_cycle as well.

For example:

GTS_cycle: 1

GSR_cycle: 1

GWE_cycle 1

LCK_cycle: 2

DONE_cycle: 4

AR# 11004
Date Created 08/29/2007
Last Updated 12/15/2012
Status Active
Type General Article