cx25840 Conexant Systems, Inc., cx25840 Datasheet - Page 73

• Manufacturer Part Number: cx25840
• Description: Video Decoder And Broadcast Audio
• Manufacturer: Conexant Systems, Inc.

CX25840/1/2/3 Data Sheet
3.6.6
3.6.7
102284B
8/3/05
Custom Data Transmission of VBI Data
Miscellaneous VBI Configuration
For each control register, the fieldname is defined as an 8-bit value with the most
significant nibble of the fieldname used to indicate the odd field and the least
significant nibble used define the even field. To program the VBI engine to decode a
specific standard or a particular line, both the odd and the even registers of the
fieldname must be programmed to decode that set standard.
For example, upon reset, VBI_LINE_CONTROL4 (0x427) register is set to a default
value of 0x00b or “No VBI data slicing” on line 4 for odd or even field. However, if
the user wished to decode line 4 from the odd video field with WST525 and the even
video field of line 4 with Gemstar 1x, then VBI_LINE_CONTROL4 would need to be
programmed as 0x47. For a complete list of options, refer to the description of the
various VBI registers in
The VBI decoding block also provides the flexibility for the user to define each
parameter through various registers and fieldnames. Once programmed, the decoder
extracts the VBI information from the video stream and outputs the decoded data to
the video output formatter (VOF) block or to the memory-mapped registers. To
initiate custom program mode, the control register, VBI Line Control {1:17}, for a
particular line must be set to Custom VBIx mode.
Three programmable registers are available for customization and are autoconfigured
by default. These registers, VBI Custom{1:3} Horizontal Delay, VBI Custom{1:3}
Time-out, and VBI Custom{1:3} Increment, can be custom-configured individually to
support specific user-defined VBI requirements. In the default configuration, the VBI
Custom 1 registers are set to decode Closed Caption 525; VBI Custom 2 registers are
set to decode WSS625; and VBI Custom 3 registers are set to decode WST525,
System C.
Each of these registers can be custom-configured through the two-wire serial
communications port or VIP host interfaces. Refer to
settings and their fieldnames. Each of these fieldname values is programmable and
allows the user to custom-modify the VBI decode engine. The other two custom
setting registers and fieldnames can be found in the register section.
Additionally, there are miscellaneous configuration registers, VBI Miscellaneous
Config 1, TTX Packet Address {1:3} (0x43C to 0x43F), used to customize Teletext
decoding and reset the VBI FIFOs for Gemstar 1x/2x, WSS, and CC. In the case of
Teletext decoding, the upper and lower limits of the Teletext packet information can
be specified through these registers and fieldnames, as well as the programming of
alternative framing packets. Furthermore, the registers can be programmed to enable
hamming comparison.
Alternatively, the miscellaneous configuration registers can also be used for
modifying the parameters in the predefined or autoconfiguration modes. A different
frame code can be substituted for the autoconfiguration mode with little user effort.
For example, modifying the VBI Alternate Frame Code Type (0x439) register, bits
FC_ALT1_TYPE, with the same code as the VBIMODE, does this.
Conexant
Section 5
of this document.
Section 5
Detailed Functional Description
for the Custom{1:3}
3-47