Answers Database

M1 9500: How to use global clock nets


Record #1489

Product Family:  Hardware

Product Line:  9500

Problem Title:
M1 9500: How to use global clock nets


Problem Description:
Keywords:  bufg, clock buffer, global clock, 9500, internal clock

Urgency:  Standard

General Description:  How can I force the fitter to use the
global clock resources?

Note:  for the global clock buffers to be used there can be
no logic between the BUFG and the CLK pins of the flip flops.


Solution 1:

An internal clock signal can't be connected directly
to the input of a global clock buffer (BUFG).  The signal must
first go through the dedicated Global Clock Pad, and then come
back in as the global clock through the BUFG.

To source a BUFG with an internally generated signal, use the
following configuration with and OBUF -> BUFG.	This will
trick the fitter into using one of the dedicated PADS
associated with the global clock buffer.

Using this method will not allow you to use this pin on the
device.




Solution 2:

If the signal is generated external to the device, simply
use an IPAD -> BUFG for schematic.

You can also LOC the signal down to one of the GCK pins.



End of Record #1489