Analog Devices ADV7850 Hardware Manual page 251

Function
alt_sat_uv_man
0 
1
alt_sat_uv, Addr 44 (CP), Address 0x3E[0]
This control is used to define the Cr and Cb saturation range. Refer to the description of alt_sat_uv_man for additional details.
Function
alt_sat_uv
0 
1
CP Peak Active Video Readback
The ADV7850 provides circuitry that monitors the active CP video on a field basis and records the largest value encountered during this
time. It is intended to be used in a peak-white type AGC for signals that do not have an embedded horizontal synchronization pulse, and
to provide feedback on the accurate function of the built-in AGC loop.
The ADV7850 itself does not provide a peak-white AGC. It merely monitors the input signal for the largest data value encountered in
each of the three channels, and presents those three values for readback via the I
no averaging or filtering before the peak detection.
Notes:
• The measurement is taken on a field basis (from one vertical synchronization to the next). The read out at any time refers to the
previous field, not necessarily the current one.
•
The tap-off point for the measurement is right after the gain multipliers. This means that clamping and AGC/manual gain have
an effect on the results.
• The peak video readback is calculated according to
where:
VtoCode is the voltage to ADC code conversion – for ADV7850 it is 4096/1.111 V
GAIN is an AGC-gain or manual gain set by the user, or an automatic gain in non embedded-sync-mode
(depending on the mode used)
pkv_cha[9:0], Addr 44 (CP), Address 0xED[5:4]; Address 0xEE[7:0] (Read Only)
This readback displays the maximum signal level measured during the active video on channel A.
Function
pkv_cha[9:0]
xxxxxxxxxx
pkv_chb[9:0], Addr 44 (CP), Address 0xED[3:2]; Address 0xEF[7:0] (Read Only)
This readback displays the maximum signal level measured during the active video on channel B.
Rev. A May 2012
Description
Range of saturator on Cr and Cb channels determined by op_656_range and alt_data_sat
Range of saturator on Cr and Cb channels determined by alt_sav_uv if op_656_range or
alt_data_sat set to 0
Description
Range of saturators on channels Cr and Cb is 15 to 235
Range of saturators on channels Cr and Cb is 16 to 240
Equation
Peak active video readback value =
(Peak video ampl – Clamp level) * VtoCode * GAIN * (1/8)
Equation 12: Peak Active Video Readback Value
Description
Readback value
C. The values are given in an unsigned format. There is
2
12.
251
ADV7850