Components should be according to the supply voltage, digital and analog circuit size, speed, current group, to avoid interfering with each other.
Circuit board when installed on both digital and analog circuits, two completely separate circuit of the ground and power supply system, conditions in digital circuits and analog circuits at different layers. On the Circuit Board needed to construct a fast, medium-speed and low-speed logic circuit, close to the connector should be placed in the range, and low-speed logic and memory, should be placed away from the connector scope. This will help reduce the common impedance coupling, decrease of radiation and cross. Clock circuits and harassment is the main source of high frequency circuit, be sure to arrange a separate, far away from the sensitive circuits.