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Service Manual
'ViewSonic
VG150
April 1999 - Version 1.0
THEORY OF CIRCUIT OPERATION
OSD mixer
In the OSD mixer block, the AM100 mixes the normal output RGB signal with the
OSD signal. The OSD output data is generated based on the RLOSD G_OSD and
B_OSD pins as well as the OSD Intensity data in EEPROM entry. When the
EN_OSD is active high, the OSD is active, and the AM100 will send the OSD data
to the LCD panel. The OSD has 16 different color schemes based on the
combinations of the three OSD color pins and the OSD Intensity data. When
R_OSD=1, OSD_Intensity=0, the AM100 will output 128 to the output red channel,
R_OUT. When R_OSD=1, and OSD Intensity=1, the AM100 will output 255. The
same scheme is used for G-OSD to G-OUT and for B-OSD to B_OUT.
EEPROM interface
As mentioned in previous sections, the external EEPROM stores much crucial
information for the AM100 internal operations. The AM100 interfaces with the
EEPROM through a 2-wire I'C serial interface. The suggested EEPROM device is
an industry standard serial-interface EEPROM (24x08). The |?C interface scheme
is briefly described here and detail description can be found in many public
literatures.
Input Mode Dependent Data
Symbol
640 | 640 | 720 | 640 | 800 | 1024 | Description
.
x
x
x
x
x
x
350 | 400 | 400 | 480 | 600 | 768
VPW
11 | OOH | 20H | 40H | 60H | 80H | AOH | LCD VSYNC pules width
01H | 21H | 41H | 61H | 81H | A1H
VBP
11 | 02H | 22H | 42H | 62H | 82H | A2H | LCD VSYNC back porch
03H | 23H | 43H | 63H | 83H | A3H | (including VPW)
VBP source|
11
04H | 24H | 44H | 64H | 84H | A4H
|LCD
VSYNC_
back
porch
05H
| 25H | 45H | 64H | 85H | ASH | (Source equivalent)
round up
Target Skip}
11
| O6H | 26H | 46H | 66H | 86H | ASH | If VBP
can not be converted
Pixel
07H | 27H | 47H | 66H | 87H | A7H | into source evenly, the leftover
is converted
into
number
Of
pixels
VSIZE
11 | O8H | 28H | 48H | 68H | 88H | A8H | LCD number of line
O9H | 29H | 49H | 69H | 89H | ASH
HPW
11.
| OAH | 2AH | 4AH | GAH } BAH | AAH | LCD HSYNC pules width
OBH | 2BH | 4BH | 6BH | 8BH | ABH
Page 18
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