Texas Instruments OMAP36 Series, Техническое справочное руководство

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Display Subsystem Functional Description
• Reset every two lines
• Reset every two fields
• Reset every eight fields
The DSS. VENC_C_PHASE register can be used to adjust the SCH (subcarrier to horizontal sync phase).
The DSS. VENC_BSTAMP_WSS_DATA [6:0] BSTAP bit field sets the amplitude of the color burst. The
DSS. VENC_M_CONTROL [1] PAL bit enables phase alternation line encoding.
A phase switching subcarrier is generated to encode the chrominance signal when the
DSS.
VENC_M_CONTROL [1] PAL bit is set to 1. Otherwise, a normal subcarrier is generated. Phase
alternation line refers to the encoding scheme in which the subcarrier alternates between two phases
every scan line. Two possible alternation sequences are possible, and the DSS.
VENC_M_CONTROL [5]
PALPHS bit selects one of these sequences.
7.4.7.5 Closed Caption Encoding
The encoder can be programmed to encode closed-caption data and extended data in the selected line.
The closed-caption data are sent to the encoder through the L4 interconnect. The data stream consists of
7-bit US-ASCII code and 1 odd-parity bit (see
Table 7-41 ).
Table 7-41. Closed-Caption Data Format
MSB LSB
Bit6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 Odd parity
The standard service encodes closed caption in both fields; the extended service encodes closed caption
in even fields. When set to 1, the DSS.
VENC_L21_WC_CTL L21EN[0] bit enables closed-caption
encoding in odd fields. When set to 1, the DSS. VENC_L21_WC_CTL L21EN[1] bit enables closed-caption
encoding in even fields.
To select the scan line where the CC data are encoded, program the VENC_LN_SEL [4:0] SLINE bit field.
CAUTION
The setting of the value of the SLINE[4:0] bit field depends on the video
standard:
• PAL mode: Because there is a one-line offset, program the desired line
number – 1. To activate the closed caption on line 21 (0x15), program the
value 0x15 – 1 = 0x14. The default value is 0x15 + 1 = 0x16 (line 22).
• NTSC mode: Because there is a four-line offset, program the desired line
number – 4. To activate the closed caption on line 21 (0x15), program the
value 0x15 – 4 = 0x11. The default value is 0x15 + 4 = 0x19 (line 25).
The DSS. VENC_LN_SEL [25:16] LN21_RUNIN bit field should be kept at reset value (0x10B). Four
closed-caption data registers contain the data to be encoded. The DSS. VENC_LINE21 [15:8] L21O and
DSS. VENC_LINE21 [7:0] L21O bit fields contain the first and the second bytes, respectively, of
closed-caption data to be encoded in the odd field. The DSS. VENC_LINE21 [31:24] L21E and
DSS. VENC_LINE21 [23:16] L21E bit fields contain the first and the second bytes, respectively, of data to
be encoded in the even field.
Immediately after the closed-caption data is written to the registers, in either the odd field or even field, the
corresponding closed-caption status bit (DSS.
VENC_STATUS [4] CCE or DSS. VENC_STATUS [3] CCO) is
reset to 0 to indicate that the closed-caption data is available in the closed-caption data registers and yet
to be encoded.
Immediately after the closed-caption data is encoded, the DSS. VENC_STATUS [4] CCE bit or the
DSS. VENC_STATUS [3] CCO bit is set to 1 to indicate that the closed-caption data has been encoded and
is ready to accept new data. As seen in Figure 7-107 , a null character is automatically inserted if the
closed-caption data is not written to the closed-caption data registers in time for encoding.
1693 SWPU177N – December 2009 – Revised November 2010 Display Subsystem
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