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Advantech COM-Express Carrier Board Design Guide Addendum Com port Chassis ground COMExpress bead bead LPC_AD[0] bead LPC_AD[1] LPC_AD[2] LPC_AD[3] LPC_FRAME# 1 2 3 Super I/O Transmitter Reciver bead LPC_DRQ[0] bead LPC_DRQ[1] bead LPC_SERIRQ 4 5 6 7 8 9 bead bead LPC_CLK 180p D-Sub 9 Figure 2-53 Serial Bus Connection 2.12.4.2 PS/2 Keyboard and Mouse For a general design consideration, the keyboard and mouse should be far away from audio and VGA signal traces to avoid crosstalk. According to the general keyboard and mouse power specifications, the traces of keyboard and mouse power trace should be routed to afford 1A. The power can be Vcc main power, or 5VSB if wake-up from S3 is needed. The reference schematic is shown in Figure 2-54. COMExpress Super I/O VCC 1A Trace Wide Ferrite Fuse 1A Bead Keyboard Connector Mini-dim 6P VCC LPC_AD[0] LPC_AD[1] LPC_AD[2] LPC_AD[3] LPC_FRAME# LPC_DRQ[0] KBDAT KBCLK KB_DAT KB_CLK LPC_DRQ[1] GND LPC_SERIRQ LPC_CLK Digital Ground Chassis Ground Mouse Connector VCC 1A Trace Wide Mini-dim 6P Ferrite Fuse 1A MS_DAT MS_CLK Bead VCC MSDAT MSCLK GND Figure 2-54 Keyboard and Mouse connection To avoid EMI and ESD, the ground plane of the keyboard / mouse connector and other digital ground planes, should be separated with an isolation moat, which is recommended to be at least 40 mils in width. Digital ground and chassis ground should be connected via screw holes to assure the integrity of the ground plane. 59
