Clock Control Block Definition

The Clock Control Block controls each global and regional clock in supported device ( Arria^® series, Cyclone^® IV, Stratix^® IV, and Stratix^® V ) families, allowing you to select between clocks on every clock network and dynamically power down the clock network. Although the Fitter automatically implements Clock Control Blocks during placement of the design, if you want to control the clocks in a design or power down a clock network, you must instantiate a Clock Control Block using the altclkctrl megafunction.

When selecting the clock source, you can select between two different PLLs clock outputs, two clock outputs of the same PLL, two clock pins, or a combination of clock pins and PLL clock outputs. The inclk[0] and inclk[1] ports of the Clock Control Block need to be driven by clock pins and the inclk[2] and inclk[3] ports need to be driven by a PLL clock output.