Philips HDRW720 Service Manual page 167

Circuit-, IC descriptions and list of abbreviations
9.6 Service UART Interface
Logic IC 74HCT14D (item 7111) is used to make a level
conversion from microprocessor (LVTTL) to +/-5V (compatible
with most RS232 interfaces) and vice versa. The control line
MPIO19_CTL_SERVICE is used to activate service and
diagnostic SW at start up procedure. The connectivity is
provided via an external service tool.
9.7 EPG Nafta Board
9.7.1 General
Two ASICs from Gemstar, GS501 (item 7100) and GS502
(item 7201), generate the EPG OSD. The host P controls both
9.7.2 Loop trough
For 'Loop Trough' the input video signals (CVBS, YC, YUV, and
YUV-progressive) from the Digital board are passing three
video switches before going to the Analog board.
• Item 7503 for CVBS and Y/C.
• Item 7502 for YUV-interlaced.
• Item 7501 for YUV-progressive.
9.7.3 EPG RGB Video
A V-sync and H-sync (for progressive = 2H-sync) are
necessary for outputting an RGB video. A sync separator (item
7703) generates these syncs. Input for the sync separator is
either the 1fh or the 2fh luminance signal from the Digital board.
A video switch (item 7700) makes the selection. For
progressive video, the signal must be attenuated (item 7701).
HDRW720/0x, DVDR725H/0x
ICs via the I2C bus (pins 45 and 48). A RAM memory (item
7102) and a Flash memory with the firmware (item 7101)
belong also to the periphery of these ASICs.
A PIC processor (item 7303) generates the POR_N reset for
this system. The POR_DC reset comes from the set, and is
active after AC power 'on'. A port expander from the host,
controls the EXT_RESET signal. This port expander (item
7200) is also used for switching the video paths on the EPG
board.
Either the board works in 'Loop Trough' mode, or (for EPG) the
output path is switched to the 'EPG RGB' video.
Figure 9-8
The RGB signal goes via emitter followers (items 7202, 7203,
and 7204) to an RGB-to-YUV converter and to an RGB-to-
CVBS, Y/C converter.
The RGB-to-YUV converter consists of four OpAmp's, which
are necessary for RGB/YUV conversion (item 7600-B, -C, and
-D) and for adding the C-sync to the Y signal (item 7600-A).
The RGB-to-CVBS, Y/C conversion is realized by IC7602. The
oscillator (item 7601) is necessary for generating the chroma
carrier.
With transistor 7603 the conversion stages can be switched
'off' for power saving.
For the PIP (Picture in Picture) feature, the D_CVBS video
signal from the Digital board is used. This signal is fed to Pin 10
of IC7201. For scanning the EPG data, the A_YCVBS signal
from the Analogue board is fed to pin 8 of IC7201.
9. EN 167