ViewSonic VG800-2 Service Manual page 38

3. Image Processor
ICM11(gm5020) is an all-in-one image processor for displays with a dual (analog and
digital)interface supporting resolutions up to SXGA. It provides integrated ADC/PLL and a DVI
compliant TMDS receiver,a high quality zoom and shrink scaling engine,frame rate conversion,an
on-screen display(OSD) controller,a microprocessor and many other functions in a single device. This
high level of integration enables simple ,flexible, cost effective solutions with fewer required
components. .
The gm5020 chip has three ADC's (analog-to-digital converters), one for each color (red,
green, and blue) and supports digital separate sync (HSYNC/VSYNC), digital composite
sync,and analog composite sync (also known as sync-on-green, or SOG). All sync types are
supported without the need for external sync separation / extraction circuits.
The gm5020 features four clock inputs. All additional clocks are internal clocks derived
from one or more of these four, using Direct Digital Synthesis (DDS).
TCLK is generated using an external crystal (recommended) or an external clock oscillator.
(1) Input Clock (TCLK). The external connection to the oscillator is via the TCLK and
XTAL pads. A 14.3MHz crystal source is recommended, as internal PLL and logic
circuits derive the required clock frequencies from this single source by default. Other
crystal frequencies may be used , but require custom bootstrapping and programming. In lieu of
using a crystal oscillator, XTAL can be driven by a single-ended TTL/CMOS input clock (e.g.
for testing of the IC) – the TCLK pin should be grounded through a 2.7k pulldown resistor to
maintain the correct duty cycle for the clock.
(2) TMDS Differential Input Clock (RC+ and RC-)
(3) Video Clock (VCLK) input pin
(4) Host Interface Transfer Clock (HCLK for 6-Wire nibble; SCL for 2-wire serial)
The gm5020 has an Input Format Measurement block (the IFM) providing the capability of
measuring the horizontal and vertical timing parameters of the input video source. This
information may be used to determine the video format and to detect a change in the input
format. It is also capable of detecting the field type of interlaced formats.
The IFM features a host programmable reset, separate from the regular gm5020 soft reset.
This reset disables the IFM, reducing power consumption. The IFM is capable of operating
while gm5020 is running in power down mode.
Horizontal measurements are measured in terms of the selected IFM_CLK (either T_CLK
or R_CLK/4), while vertical measurements are measured in terms of HSYNC pulses.
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