Configuration Clock Source
Specifies the clock source for device initialization (the duration between
CONF_DONE signal went high and before INIT_DONE
signal goes high). In 20nm or prior device families, three options are available when AS
x1 or AS x4 configuration mode is not selected, which are Internal
Oscillator (default value), DCLK pin, and
CLKUSR pin.
For AS x1 or AS x4 configuration mode, you can select either tInternal Oscillator or CLKUSR pin only. The DCLK pin is an illegal option for AS mode. In 14nm device families, only Internal Oscillator or OSC_CLK_1 pins are available.