Bt860/861
3.0 Digital Processing and Functionality
3.1 Video
Multiport YCrCb to NTSC/PAL /SECAM
3.1.5 Subcarrier and Burst Generation
The Bt860/861 uses a 32-bit subcarrier increment to synthesize the subcarrier.
The value of the subcarrier increment required to generate the desired subcarrier
frequency for NTSC and PAL formats is found by:
32
M_SC_DR[31:0] = int (2 × f / f + 0.5)
sc clk
where f is the encoder system clock rate and f is the desired subcarrier
clk
sc
frequency.
When available, use the relationship between HCLK and the subcarrier frequency
as given in ITU-R BT.470. For example:
32
NTSC-M: M_SC_DR[31:0] = int {[455 / (2 × HCLK)] × 2 + 0.5}
32
PAL-B: M_SC_DR[31:0] = int {[(1135 / 4 + 1 / 625) / HCLK] × 2 + 0.5}
Tables 3-2 and 3-3 lists the programming values for common NTSC and PAL
standards.
For SECAM formats, the two subcarrier frequency increments are defined by:
32
SECAM Dr: M_SC_DR[31:0] = int [(f / f ) × 2 + 0.5]
sc clk
32
SECAM Db: M_SC_DB[31:0] = int [(f / f ) × 2 + 0.5]
sc clk
Table 3-4 lists standard programming values for SECAM.
The HBURST_BEG register determines the start of burst (or subcarrier for
SECAM). In PAL and NTSC video formats the HBURST_END register
determines the end of the burst. The BURST_AMP register controls burst
amplitude. The burst is automatically blanked during the horizontal sync to
prevent generation of invalid sync pulses. Burst blanking is automatically
controlled and depends on which video format is selected. Burst rise and fall
times are internally controlled.
The SC_AMP register controls the SECAM subcarrier amplitude. In addition,
generation of the “bottleneck signals” for subcarrier line synchronization may be
enabled using the FIELD_ID register bit. Registers PROG_SC and
SC_PATTERN allow control of active line placement and subcarrier phase
sequencing.
D860DSA
Conexant
3-11
CONEXANT [ CONEXANT SYSTEMS, INC ]
