Letterbox Detection - Analog Devices ADV7850 Hardware Manual

Function
sdp_free_run_man_col_
en
1 
0
sdp_free_run_cbar_en, Addr 90 (SDP), Address 0xDD[1]
This control is used to select the color bar pattern to be output in manual free run mode.
Function
sdp_free_run_cbar_en
1
0 
sdp_force_free_run, Addr 90 (SDP), Address 0xDD[0]
This control is used to force free run mode irrespective of the input lock status.
Function
sdp_force_free_run
1
0 
sdp_free_run_y[7:0], Addr 90 (SDP), Address 0xDE[7:0]
This control is used to set the luma level to output in free run mode if sdp_free_run_man_col_en is set to 1.
sdp_free_run_v[3:0], Addr 90 (SDP), Address 0xDF[7:4]
This control is used to set the V level to output in free run mode if sdp_free_run_man_col_en is set to 1.
sdp_free_run_u[3:0], Addr 90 (SDP), Address 0xDF[3:0]
This control is used to set the U level to output in free run mode if sdp_free_run_man_col_en is set to 1.
6.17

LETTERBOX DETECTION

Incoming video signals can conform to different aspect ratios (16:9 wide screen of 4:3 standard). For transmissions in the wide screen
format, a digital sequence (WSS) is transmitted with the video signal. If a WSS sequence is provided, the aspect ratio of the video can be
derived from digitally decoded bits contained within it.
In the absence of a WSS sequence, the letterbox detection can be used to find wide screen signals. The detection algorithm examines the
active video content of lines at the start and at the end of a field. If the presence of black lines is detected, this can serve as an indication
that the currently shown picture is in wide screen format.
The active video content (luminance magnitude) over a line of video is summed together. At the end of a line, this accumulated value is
compared to a threshold and a decision is made whether or not a particular line is considered to be black. The threshold value needed can
depend on the type of input signal, and some control is provided via sdp_lbox_thr[4:0].
Rev. A May 2012
Description
If in free run, output manual luma and chroma values set by sdp_free_run_y, sdp_free_run_v,
and sdp_free_run_u
If in free run, output decoded video data
Description
If in free run mode, output color bar data
If in free run mode, output free run mode data
Description
Force free run
Normal operation
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ADV7850