The initialization clock source is from the internal oscillator, CLKUSR pin, or DCLK pin. By default, the internal oscillator is the clock source for initialization. If you use the internal oscillator, the Cyclone® V device will be provided with enough clock cycles for proper initialization.
The CLKUSR pin provides you with the flexibility to synchronize initialization of multiple devices or to delay initialization. Supplying a clock on the CLKUSR pin during initialization does not affect configuration. After the CONF_DONE pin goes high, the CLKUSR or DCLK pin is enabled after the time specified by tCD2CU . When this time period elapses, Cyclone® V devices require a minimum number of clock cycles as specified by Tinit to initialize properly and enter user mode as specified by the tCD2UMC parameter.
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