CX25870/871
1.0 Functional Description
Flicker-Free Video Encoder with Ultrascale Technology
1.3 Device Description
Table 1-24. Serial Writes Required to Switch CX25870/871 into SCART Output Operation
Bit Name
EN_SCART
Location
Value
Comment
Bit 3–Register 0x6C
1
Enables SCART Output mode. DACs will transmit Video[0-3] as
SCART compatible RGB/CVBS outputs.
By default, in SCART Output mode, the CX25870 will transmit:
DAC_A = Video[0] = Red
DAC_B = Video[1] = Green
DAC_C = Video[2] = Blue
DAC_D = Video[3] = PAL Composite (CVBS)
OUT_MUXD[1:0]
OUT_MUXC[1:0]
OUT_MUXB[1:0]
OUT_MUXA[1:0]
Bits 7:0–Register CE
Bits 3:2–Register D6
E4
11
By configuring the DAC routing register, the CX25870 will now
transmit:
DAC_A = Video[0] = 00 = Red
DAC_B = Video[1] = 01 = Green
DAC_C = Video[2] = 10 = Blue
DAC_D = Video[3] = 11 = PAL Composite (CVBS)
OUT_MODE[1:0]
Forces CX25870 to generate SCART output mode.
NOTE: No change to the incoming or outgoing HSYNC* and VSYNC* signal
frequencies are necessary for SCART generation. The sync rates should
continue to match those found with PAL-BDGHI transmission.
While the CX25870/871 is in SCART outmode, the composite video output
(Video[3]) contains a standard bilevel analog sync along with all other
components that comprise a standard PAL-BDGHI video signal. The sync pulse
has an amplitude of 0 mV to 300 mV peak-to-peak and a duration of 4.70 µs by
default. The amplitude can only be adjusted through the use of external passives,
but its width can be adjusted through serial writing of the CX25870
HSYNC_WIDTH register.
The CX25870’s Composite should be used by the subsystem to provide the
positive-going Video output/sync output expected by SCART-compliant display
devices. In other words, the PAL Composite output should be fed into the Video
Input (Contact #20-CEI IEC 933-1) on the SCART connector. CVBS will possess
the same bandwidth and time delays as the CX25870 RGB primary color signals.
The inclusion of a full composite video signal as the 4th output exceeds the
SCART capabilities of some non-Conexant Flicker Filter encoders which choose
to output only Composite Sync as the 4th output. This implementation benefits
the customer because some European Set-Top Boxes connect to TVs solely
through the SCART connector. If the TV only receives Composite video via the
SCART connector, and the Set Top Box is set to RGB output with sync for
blanking (not CVBS) on pin 20, a picture will not be present at all on the TV.
However, with the CX25870, if the TV only receives CVBS (not RGB) and the
Set Top Box is set to RGB output with CVBS on pin 20 the customer will get a
colorful picture on his TV.
100381B
Conexant
1-77
CONEXANT [ CONEXANT SYSTEMS, INC ]
