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XC3000/XC4000: Can I source ACLK/GCLK from internal logic? BUFGS, BUFGP?


Record #116

Problem Title:
XC3000/XC4000: Can I source ACLK/GCLK from internal logic? BUFGS, BUFGP?


Problem Description:



Solution 1:




Users are sometimes concerned that global buffer resources are either not
accessible from internal logic, or that the use of one with internal logic
forces the wasting of an input pin.  The following summarizes this for the
different families of FPGAs:

2k:  You can source either ACLK or GCLK from internal logic at no cost,
     i.e. no IOB is used up.

3k:  You can source either ACLK or GCLK from internal logic at no cost.

4k:  You can source BUFGS from internal logic at no cost, but
     sourcing BUFGP internally uses up the IOB dedicated for that clock
     buffer.





End of Record #116