Posted on May 29, 2015 at 21:42It allows for a broader selection of crystals to be used in the design. Understand that crystals can be cut in different directions, and have different resistive and capacitive characteristics. You'd need to review a few crystal specs from a couple of manufactures to understand the options. The boards could also use crystal of different frequencies, 8 MHz is one option, but there are magic values that work for TV frequencies, or baud rates, ethernet, etc. Most of the EVAL series boards use 25 MHz HSE for Ethernet use cases, the DISCO/NUCLEO boards typically derive 8 MHz from an oscillator source provided by the ST-LINK chip. The F4-DISCOs are one of the few that have an 8 MHz crystal and parts placed on main processor.
