AR# 1836: The oscillator in the 4000 FPGA is disabled (if OSC4 unused) after configuration.
The oscillator in the 4000 FPGA is disabled (if OSC4 unused) after configuration.
What happens to the oscillator in the XC4000 family of FPGAs after configuration?
If the Oscillator isn't used, meaning that the OSC4 library symbol is not used in the input design, the oscillator is disabled to preserve power consumption. This means, that the oscillator is not oscillating after configuration if the oscillator component is not being used in the design.