GS2961A Datasheet, PDF (42/104 Pages) Gennum Corporation – Ancillary data extraction

4.10.1 Manual Switch Line Lock Handling
The principle of switch line lock handling is that the switching of synchronous video
sources will only disturb the horizontal timing and alignment, whereas the vertical
timing remains in synchronization - i.e. switching between video sources of the same
format.
To account for the horizontal disturbance caused by a synchronous switch, the word
alignment block and timing signal generator automatically re-synchronizes to the new
timing immediately if the synchronous switch happens during the designated switch
line, as defined in SMPTE recommended practice RP168-2002.
The device samples the SW_EN pin on every PCLK cycle. When a Logic LOW to HIGH
transition on this pin is detected anywhere within the active line, the word alignment
block and timing signal generator re-synchronize immediately to the next TRS word.
This allows the system to force immediate lock on any line, if the switch point is
non-standard.
To ensure proper switch line lock handling, the SW_EN signal should be asserted HIGH
anywhere within the active portion of the line on which the switch has taken place, and
should be held HIGH for approximately one video line. After this time period, SW_EN
should be de-asserted. SW_EN should be held LOW during normal device operation.
NOTE: It is the rising edge of the SW_EN signal, which generates the switch line lock
re-synchronization. This edge must be in the active portion of the line containing the
video switch point.
Video source 1
EAV
ANC
SAV
ACTIVE PICTURE
Switch point
EAV
ANC
S AV EA V ACTIVE PAINCCTUR E
EAV
ANC
SAV
ACTIVE PICTURE
EAV
ANC
SAV
Video source 2
DATA IN
EAV
ANC
SAV
ACTIVE PICTURE
EAV
ANC
SAV E AV ACTIVE PAINCCTUR E
EAV
ANC
EAV
ANC
SAV
ACTIVE PICTURE
EAV
ANC
SAV
switch video source 1 to 2
ACTIVE PICANTUCRE
EAV
ANC
SAV
SAV
ACTIVE PICTURE
ACTIVE PICTURE
EAV
ANC
SAV
EAV
ANC
SAV
DATA OUT
TRS position
SW_EN
EAV
ANC
SAV
ACTIVE PICTURE
EAV
ANC
SAV
ACTIVE PICANTUCRE
EAV
ANC
SAV
ACTIVE PICTURE
EAV
ANC
SAV
Re - s y n c hronization
Video source 1
Video source 2
DATA IN
Switch point
EAV
ANC
SAV
ACTIVE PICTURE
EAV
ANC
S AV EA V ACTIVE PAINCCTUR E
EAV
ANC
SAV
ACTIVE PICTURE
EAV
ANC
SAV
EAV
ANC
SAV
EAV
ANC
SAV
ACTIVE PICTURE
ACTIVE PICTURE
EAV
EAV
ANC
ANC
SAV E AV ACTIVE PAINCCTUR E
EAV
ANC
SAV
ACTIVE PICTURE
EAV
ANC
SAV
switch video source 2 to 1
SAV
ACTIVE PICTURE
EAV
ANC
SAV
ACTIVE PICTURE
EAV
ANC
SAV
DATA OUT
EAV
ANC
SAV
ACTIVE PICTURE
EAV
ANC
SAV
ACTIVE PICTURE
EAV
ANC
SAV
ACTIVE PICTURE
TRS position
SW_EN
Figure 4-11:Switch Line Locking on a Non-Standard Switch Line
Re - s y n c hronization
EAV
ANC
SAV
GS2961A 3Gb/s, HD, SD SDI Integrated Receiver
Data Sheet
54385 - 2
September 2012
42 of 104