845GL datasheet(132/193 Pages) INTEL

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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

Sync on Green

HSYNC

VSYNC

Voltage

LVTTL

Enable/Disable

Port control

Polarity adjust

VGA or port control

Composite Sync Support

Special Flat Panel Sync

Stereo Sync

DDC

Voltage

3.3 V – may need to be externally

buffered to 5 V

Control

Through GPIO interface

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