Analog Devices ADV7850 Hardware Manual page 248

An error signal is derived from the comparison of the measured synchronization depth and the target value. The error signal is weighted
by a factor that allows different response times to be selected (agc_tim[2:0] is used to select different time constants). The resulting gain
value is applied to all three channels A, B, and C.
agc_freeze allows the AGC loop to be stopped, that is, frozen. If frozen, the currently active gain is no longer updated but is applied
continuously to all three datastreams.
hs_norm, Addr 44 (CP), Address 0x71[3]
This control is used to select the nominal HSync depth.
Function
hs_norm
0 
1
agc_tar_man, Addr 44 (CP), Address 0x71[5]
This control is used to enable the manual target level.
Function
agc_tar_man
0 
1
agc_tar[9:0], Addr 44 (CP), Address 0x71[7:6]; Address 0x72[7:0]
This control is used to enable the manual AGC target value. It is used to set the target value for the horizontal synchronization depth
after gain is applied. It is an unsigned value.
Function
agc_tar[9:0]
0x000 
0x3FF
agc_freeze, Addr 44 (CP), Address 0x71[4]
This control is used to enable AGC freeze.
Function
agc_freeze
0 
1
agc_tim[2:0], Addr 44 (CP), Address 0x71[2:0]
This control is used to select the AGC time constant.
Rev. A May 2012
Description
AGC target scales video as per 300 mV horizontal synchronization depth
AGC target scales video as per 286 mV horizontal synchronization depth
Description
AGC operates based on 300 mV or 286 mV horizontal synchronization depth, use hs_norm to
select
AGC operates based on agc_tar[9:0]
Description
Minimum range,
...
Maximum range
Description
AGC loop operational.
AGC loop frozen and not updated further. Last gain value becomes static.
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ADV7850