Analog Devices ADV7850 Hardware Manual page 300

Function
ch1_f_run_thr[2:0]
000
001
010
011
100 
101
110
111
ch2_f_run_thr[2:0], Addr 44 (CP), Address 0x43[2:0]
This control is used to select the free run threshold for sync channel 2. It determines the horizontal conditions under which free run
mode is entered or left. The length of the incoming video line is measured based on the crystal clock and compared to an internally
stored parameter. The magnitude of the difference decides whether or not sync channel 2 will enter free run mode.
Function
ch2_f_run_thr[2:0]
000
001
010
011
100 
101
110
111
ch1_fr_ll[10:0], Addr 44 (CP), Address 0x8F[2:0]; Address 0x90[7:0]
This control is used to set the free run line length in a number of crystal clock cycles in one line of video for sync channel 1 STDI. It
should be programmed only with video standards that are not supported by prim_mode[3:0] and vid_std[5:0].
Function
ch1_fr_ll[10:0]
0x000 
All other values
ch2_fr_ll[10:0], Addr 44 (CP), Address 0x47[2:0]; Address 0x48[7:0]
This control is used to define the free run line length in the number of crystal clock cycles in one line of video for sync channel 2 STDI.
This control should only be programmed for video standards that are not supported by prim_mode[3:0] and vid_std[5:0].
Rev. A May 2012
Description
Minimum difference to switch into free run is 2. Maximum difference to switch out of free run
is 1.
Minimum difference to switch into free run is 256. Maximum difference to switch out of free
run is 200.
Minimum difference to switch into free run is 128. Maximum difference to switch out of free
run is 112.
Minimum difference to switch into free run is 64. Maximum difference to switch out of free
run is 48.
Minimum difference to switch into free run is 32. Maximum difference to switch out of free
run is 24.
Minimum difference to switch into free run is 16. Maximum difference to switch out of free
run is 12.
Minimum difference to switch into free run is 8. Maximum difference to switch out of free run
is 6.
Minimum difference to switch into free run is 4. Maximum difference to switch out of free run
is 3.
Description
Minimum difference to switch into free run is 2. Maximum difference to switch out of free run
is 1.
Minimum difference to switch into free run is 256. Maximum difference to switch out of free
run is 200.
Minimum difference to switch into free run is 128. Maximum difference to switch out of free
run is 112.
Minimum difference to switch into free run is 64. Maximum difference to switch out of free
run is 48.
Minimum difference to switch into free run is 32. Maximum difference to switch out of free
run is 24.
Minimum difference to switch into free run is 16. Maximum difference to switch out of free
run is 12.
Minimum difference to switch into free run is 8. Maximum difference to switch out of free run
is 6.
Minimum difference to switch into free run is 4. Maximum difference to switch out of free run
is 3.
Description
Internal free run line length decoded from prim_mode[3:0] and vid_std[5:0].
Number of crystal clocks in ideal line length. Used to enter or exit free run mode.
300
ADV7850