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T
opfield
Bottomfield
v_sync
Field_ID
h_sync
L1=4 (NTSC)
L2
L3=21 (NTSC)
L4
L5=264 (NTSC)
L6
L7=266 (NTSC)
L8
L9=283 (NTSC)
L10
L11=1 (NTSC)
L12
Top field image start address
Bottom field VBI start address
(vertical ancillary)
Bottom field image start address
Top field VBI start address
(vertical ancillary)
Top field active video area
Bottom field active video area
Specific ancillary data
(closed caption, CGMS)
Bottom field VBI start address
(horizontal ancillary)
EAV (4 words)
Top field VBI start address
(horizontal ancillary)
SAV (4 words)
Horizontal blanking
Architecture
1773
SPRUH82C – April 2013 – Revised September 2016
Copyright © 2013–2016, Texas Instruments Incorporated
Video Port Interface (VPIF)
35.2.7.2 VBI Ancillary Data Receive
When the VBI receive function is enabled, the VPIF receives all data in the associated blanking region.
The VPIF cannot selectively receive sub-regions in the VBI space. The CPU has to receive valid data from
this data and you have to prepare for the correct size of data buffer. For example in the NTSC case, the
horizontal ancillary data needs 268 bytes × 525 lines and the vertical ancillary data needs 1440 bytes × 38
lines buffer.
The address line offset for the vertical ancillary data uses the channel
n
image data address offset register
(C
n
IMGOFFSET).
Processing Method for Specific Ancillary Data
The VPIF has the ability to capture/assert video ancillary data (
Image of Specific Ancillary Data on NTSC
)
that is not video image data but is VBI data. In most cases, video ancillary data is inserted in the blanking
interval for either the horizontal or vertical direction. But in some cases, such as CGMS or closed-caption
that is in Japanese and US applications, the line number where these kinds of ancillary data is inserted is
in the active video area. In the case that ancillary data is inserted in the active video area, the VPIF
regards the incoming (or stored data) as video data.
Image of Specific Ancillary Data on NTSC
Clipping Function for Output
The clipping function is prepared for avoidance of miss-synchronization on an external device (video
encoder), which receives output of the VPIF module. In some cases, the source data for the active video
area has a combination of FF-00-00, which is the same as TRC (synchronization code). Some video
encoders regard this combination as part of TRC and then the synchronization is failed.
In order to avoid this issue, the VPIF module is capable of clipping the output data value except the TRC
within the range of 01~FEh. If this function is activated, the value 00h is clipped to 01h and the value FFh
is clipped to FEh. Any other value is passed through.
As shown in
Data Areas and Clipping Function
, VPIF has two data areas other than TRC: one is blanking
data (ancillary data) and the second is video image data. The clipping function can be independently
enabled for each data area. Note that field-level control is not supported.
The relationship between register bit assignment and the clipping function is shown in
Assignment on Clipping Function
. Control register bits in
Register Bit Assignment on Clipping Function
are
prepared for both channel 2 and channel 3. Clipping on the channels is independently activated.