S912XEG128J2MAA Datasheet, PDF (1263/1324 Pages) Freescale Semiconductor, Inc – Microcontrollers

Appendix C PCB Layout Guidelines
Appendix C
PCB Layout Guidelines
The PCB must be carefully laid out to ensure proper operation of the voltage regulator as well as of the
MCU itself. The following rules must be observed:
• Every supply pair must be decoupled by a ceramic capacitor connected as near as possible to the
corresponding pins .
• Central point of the ground star should be the VSS3 pin.
• Use low ohmic low inductance connections between VSS1, VSS2 and VSS3.
• VSSPLL must be directly connected to VSS3.
• Keep traces of VSSPLL, EXTAL, and XTAL as short as possible and occupied board area for C7,
C8, and Q1 as small as possible.
• Do not place other signals or supplies underneath area occupied by C7, C8, and Q1 and the
connection area to the MCU.
• Central power input should be fed in at the VDDA/VSSA pins.
Example layouts are illustrated on the following pages.
Freescale Semiconductor
MC9S12XE-Family Reference Manual Rev. 1.25
1263