User manual

Advantech SOM-Express Design Guide
Chapter 5 Carrier Board Design Guidelines 57
5.4.2 Design Guidelines
VESA standards require the DDC_PWR line. Some VGA monitors do not support the
DDC standard. We suggest that VGA_I2C_CK and VGA_I2C_DAT signals must
connect to the CRT monitor. They can be used for plug and play and monitor-type
detection when standard monitors are attached.
SOM-Express
VGA_RED
VGA Connector
D-Sub15
VGA_GRN
VGA_BLU
VGA_HSYNC
VGA_VSYNC
VGA_I2C_CK
VGA_I2C_DAT
Figure 5-19 VGA Connections
5.4.3 Layout Guideline
5.4.3.1 RLC Components
The RGB outputs are current sources and therefore require 150 ohm load resistors
from each RGB line to analog ground to create the output voltage (approximately 0 to
0.7 volts). These resistors should be placed near the VGA port (a 15-pin D-SUB
connector). Serial ferrite beads for the RGB lines should have high frequency
characteristics to eliminate relative noise. The 39 ohm series damping resistors for
HSY and VSY should be placed near the D-SUB connector.
Figure 5-20 VGA Layout Guidelines