Answers Database

XC4000 Configuration: Done goes high but outputs never become active


Record #158

Problem Title:
XC4000 Configuration:  Done goes high but outputs never become active


Problem Description:



Solution 1:




If the user chooses options in makebits such that the activation of
the chip is synchronized with a user clock (uclk_sync and uclk_nosync)
and no user clock is specified in the design and/or attached to the
device, the chip could reach a point where the configuration of the
device is done and the done pin is asserted, but the outputs do not
become active.	The solution is either to recreate the bitstream
specifying the startup clock as cclk, or supply the appropriate
user clock.

In an XC4000 device, remember that by default the GSR is released two CCLKs
after the DONE pin goes high.  If you do not clock twice after DONE goes
high in serial slave mode, your outputs will forever stay in their initial
state.





End of Record #158