Advantech SOM-Express Design Guide
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Chapter 5 Carrier Board Design Guidelines
5.12.4 Application
Notes
Some signals from the Super I/O, like Serial port, Parallel port, Floppy, IR, KBC, etc.,
can connect to SOM-Express via the LPC Bus. Figure 5-54 shows the architecture of
the LPC interface. We will make some examples. You can get more information in
the Super I/O data sheet.
Figure 5-54 Architecture of LPC interface
5.12.4.1 Serial
port
Sometimes, in order to avoid EMI issues, we often separate ground to frame ground
(I/O ground). Adding beads and capacitors to the carrier board is necessary. Figure
5-55 shows the Serial Bus Connection.
frame ground
Com port
D-Sub 9
6
8
5
1
7
2
3
4
9
bead
bead
bead
bead
bead
bead
bead
bead
180p
Super
I/O
Transmitter
Reciver
SOM-
Express
LPC_AD[0]
LPC_AD[1]
LPC_AD[2]
LPC_AD[3]
LPC_FRAME#
LPC_DRQ[0]
LPC_DRQ[1]
LPC_SERIRQ
LPC_CLK
Figure 5-55 Serial Bus Connection
5.12.4.2
PS/2 Keyboard and Mouse
For a general design concept, the keyboard and mouse should be far away from
audio and VGA signal traces to avoid crosstalk. According to general keyboard and
mouse power specifications, the traces of keyboard and mouse power trace should
be routed to afford 1A. The power can be sourced from the system power plane
through a ferrite bead and then a fuse. A capacitor should be added behind, with the
ground of the capacitor place at the keyboard/mouse ground. A practical schematic is
shown in figure 5-56.
