Detailed Mechanism Of Stdi Block Horizontal/Vertical Lock Mechanism; Stdi Horizontal Locking Operation; Stdi Vertical Locking; Figure 90: Stdi Horizontal Locking Operation - Analog Devices ADV7850 Hardware Manual

ch2_sdti_dvalid is set to 1 only after four fields with the same length are recorded. As a result, STDI measurements can take up to five
fields to finish.
Function
ch2_stdi_dvalid
0 
1

Detailed Mechanism of STDI Block Horizontal/Vertical Lock Mechanism

9.7.3

9.7.3.1 STDI Horizontal Locking Operation

For the STDI horizontal locking operation, the STDI block compares adjacent line length differences (in XTAL clock cycles) with the
programmed threshold. If 128 consecutive adjacent lines lengths are within the threshold, the STDI horizontally locks to the incoming
video.
line 3-line4≦threshold? line 3-line4≦threshold?
line 1-line2≦threshold? line 1-line2≦threshold?
line 1 line 1 line 2 line 2
line 2-line3≦threshold? line 2-line3≦threshold?
Once the STDI locks to the incoming video, it registers the first BL measurement (first eight lines) as latched data (absolute line length: L)
and keeps monitoring and comparing each successive line length with the absolute line length (L/8).
The STDI horizontally unlocks if 128 consecutive lines have a line length greater than the threshold.
line 1 line 1 line 2 line 2 line 3 line 3
First 8 blocks of line length = BL read back value First 8 blocks of line length = BL read back value
Registered as "Absolute Line Length" Registered as "Absolute Line Length"

9.7.3.2 STDI Vertical Locking

The STDI block compares adjacent field length differences and VSync lengths in line counts and compares them with a threshold. If four
consecutive adjacent field lengths (LCF) and line counts in VSync (LCVS) are within the threshold, the STDI vertically locks to the
incoming video.
Rev. A May 2012
Description
Sync channel 2 STDI measurement not valid
Sync channel 2 STDI measurement valid
line 5-line6≦threshold? line 5-line6≦threshold?
line 4 line 4 line 5 line 5 line 6 line 6
line 3 line 3
line 4-line5≦threshold? line 4-line5≦threshold?
Monitors 128 consecutive lines before STDI horizontally "Lock" Monitors 128 consecutive lines before STDI horizontally "Lock"

Figure 90: STDI Horizontal Locking Operation

line 4 line 4 line 5 line 5 line 6 line 6 line 7 line 7
L L

Figure 91: STDI HSync Monitoring Operation

line 7 line 7 line 8 line 8
line 129 – L/8 ≦threshold? line 129 – L/8 ≦threshold?
line 8 line 8
"L/8" will be registered as absolute line length reference for each "L/8" will be registered as absolute line length reference for each
lines after STDI horizontally locks to the incoming video signal lines after STDI horizontally locks to the incoming video signal
274
line 128 line 128
line 131 – L/8 ≦threshold? line 131 – L/8 ≦threshold?
line 130 line 131 line 130 line 131
line 128 line 129 line 128 line 129
line 130 – L/8 ≦threshold? line 130 – L/8 ≦threshold?
ADV7850
line 129 line 129