Hardware design considerations clock

Input and output clock phase to be consistent, the cpu clock output by the external clock driver chip, to achieve a clock division multiplexing, and clock phase is the same; if the output clock frequency output not elapsed, may be input directly to the clock on-chip clock needs.
The general principles of the chip select: to select the most widely used, is not easy to stop production; manufacturer compatibility, compatibility package; PIN pin upward downward compatibility; can refer others development board.