cx25870 Conexant Systems, Inc., cx25870 Datasheet - Page 102

• Manufacturer Part Number: cx25870
• Description: Video Encoder With Adaptive Flicker Filtering And Hdtv Output
• Manufacturer: Conexant Systems, Inc.

1.0 Functional Description
1.3 Device Description
Table 1-30. Serial Writes Required to Remove Bilevel Syncs from all VGA/DAC Outputs
1-86
HDTV_EN
RASTER_SEL[1:0]
RGB2PRPB
BPB_SYNC_DIS
GY_SYNC_DIS
RPR_SYNC_DIS
NOTE(S):
+986 mV.
Bit Name
When all bits in
Tables 1-29
Bits[1:0]—Register 0x28
Bit 6—Register 0x28
Bit 4—Register 0x28
Bit 5—Register 0x28
Bit 7—Register 0x28
Bit 3—Register 0x28
and the digital data sent to the CX25870/871 must also be adjusted to ensure the
proper operation of this mode.
embedded bilevel syncs be completely absent from the RGB analog outputs.
Fortunately, the CX25870/871 can provide VESA’s ‘syncless’ outputs so long as
the additional set of bits found in
Complete all steps in
Table 1-30
286 mV DC offset because the encoder cannot generate negative voltage levels.
Therefore, the blanking level will reside at 286 mV and the maximum luminance
level is 986 mV for the 3 different outputs. The HSYNC* and VSYNC* digital
inputs received by the CX25870/871 will continue to cause blanking, but this is
irrelevant since the data itself is blanked at these times.
DAC analog output stay between 0.0 Vdc and 0.700 Vdc +.07 V (or -.03 V) with
no excursions at all times. Clearly, the blank and maximum luminance levels for
the CX25870/871 are in violation of this specification. To compensate for the DC
offset, the CX25870/871 is reliant on the VGA Monitor’s decode capabilities to
remove this DC deviation. Through testing, Conexant has determined that most, if
not all, present-day monitors have this function to filter out minor DC offsets.
Of course, the master device’s timing signals (HSYNC*, VSYNC*, CLKI)
Some applications, such as VESA compliant PC Monitors, dictate that the
and
The outputs generated from the combined steps listed in
To reiterate, the VESA Video Signal Standard specification requires that the
Other major characteristics of the CX25870/871 VGA—DAC Output Mode are:
• Acceptable digital RGB inputs include 24/16/or 15 bits per pixel
• Acceptable digital YCrCb inputs include 24/16 bits per pixel multiplexed
• CX25870 can only be a slave to the data master in this type of operation
• Sampling rate in this mode is determined based on the incoming clock
• DAC resolution for all DACs = 10-bits
Location
multiplexed or nonmultiplexed RGB
or nonmultiplexed YCrCb
frequency (CLKI)
1-30
will not contain any embedded syncs, but will contain a positive
are programmed correctly, the active video level range will be from +286 mV to
Conexant
Tables 1-29
Value
00
1
0
1
1
1
Flicker-Free Video Encoder with Ultrascale Technology
Table 1-30
plus 1-30.
DACs output HDTV compatible RGB
Default state. No need to reprogram.
Default state. No need to reprogram.
Disables sync on Blue output
Disables sync on Green output
Disables sync on Red output
are programmed as shown:
Comment
Table 1-29
CX25870/871
and
100381B