Ramdac Layout Recommendations; Hsync/Vsync Output Guidelines; Figure 52. Recommended Ramdac Reference Resistor Placement And Connections - Intel 815 Design Manual

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Figure 52. Recommended RAMDAC Reference Resistor Placement and Connections

8.1.4

RAMDAC Layout Recommendations

The primary concern with regard to the RGB signal length is that the RGB routes are matched
and routed with the correct impedance. The impedance should be 37.5 , single-ended trace
to the 75 , termination resistor. Routing from the 75
the VGA connector should be 75
The trace width for the RGB signal should be selected for a 37.5
route) to the 75
the VGA connector.
The spacing for each DAC channel routing (i.e., between red and green, green and blue
outputs) should be a minimum of 20 mils.
The space between the RGB signal route and other routes should be a minimum of 20 mils for
each DAC route.
All RGB signals should be referenced to ground.
The trace width for the HSYNC and VSYNC signal routes should be selected for an
approximately 40
The spacing between the HSYNC /VSYNC signal routes should be at least 10 mils, preferably
20 mils.
The space between HSYNC/VSYNC signal routes and other routes should be at least 10 mils,
preferably 20 mils.
Route the HSYNC and VSYNC over the ground plane, if possible. The HSYNC and VSYNC
signals should not route over or near any clock signals or any other high switching routing.
8.1.5

HSYNC/VSYNC Output Guidelines

The HSYNC and VSYNC output of the GMCH may exhibit up to 1.26V P-P noise when driven
high under high traffic system memory conditions. To minimize this, the following is required:
Add external buffers to HSYNC and VSYNC.
Examples include: Series 10
®
Intel 815 Chipset Platform Design Guide
Graphics Chip
IREF
ball/pin
Position resistor
near IREF pin.
No toggling signals
should be routed
R
set
near R resistor.
set
termination resistor. The 75
impedance.
Integrated Graphics Display Output
Short, wide route connecting resistor to IREF pin
Resistor for setting RAMDAC reference current
178 , 1%, 1/16 W, SMT, metal film
Large via or multiple vias straight down to ground plane
resistor to the video pi-filter and to
impedance.
termination resistor should be placed near
resistor with a 74LVC08
RAMDAC_ref_resistor_place_conn
impedance (single-ended
105