Datasheet

Functional Description
132 Intel
®
82845G/82845GL/82845GV GMCH Datasheet
4.5.1 Analog Display Port Characteristics
The analog display port provides a RGB signal output along with a HSYNC and VSYNC signal.
There is an associated DDC signal pair that is implemented using GPIO pins dedicated to the
analog port. The intended target device is for a CRT-based monitor with a VGA connector. Display
devices such as LCD panels with analog inputs may work satisfactory but no functionality has been
added to the signals to enhance that capability.
Integrated RAMDAC
The display function contains a RAM-based Digital-to-Analog Converter (RAMDAC) that
transforms the digital data from the graphics and video subsystems to analog data for the CRT
monitor. The GMCH’s integrated 350 MHz RAMDAC supports resolutions up to 1920x1080 at
85 Hz and 2048x1536 at 60 Hz. Three 8-bit DACs provide the R, G, and B signals to the monitor.
Sync Signals
The HSYNC and VSYNC signals are digital and conform to TTL signal levels at the connector.
Since the GMCH has 3.3 V buffers for these signals, external level shifting may be required. These
signals can be polarity adjusted and individually disabled in one of the two possible states. The
sync signals should power up disabled in the high state. No composite sync or special flat panel
sync support is included.
VESA/VGA Mode
VESA/VGA mode provides compatibility for pre-existing software that sets the display mode
using the VGA CRTC registers. Timings are generated based on the VGA register values and the
timing generator registers are not used.
Table 4-10. Analog Port Characteristics
Signal Port Characteristic Support
RGB
Voltage Range 0.7 V p-p only
Monitor Sense Analog Compare
Analog Copy Protection No
Sync on Green No
HSYNC
VSYNC
Voltage LVTTL
Enable/Disable Port control
Polarity adjust VGA or port control
Composite Sync Support No
Special Flat Panel Sync No
Stereo Sync No
DDC
Voltage
3.3 V – may need to be externally
buffered to 5 V
Control Through GPIO interface