Cp Offset Block; Figure 81: Channel A, B, And C Automatic Value Selection - Analog Devices ADV7850 Hardware Manual

Function
pkv_chb[9:0]
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pkv_chc[9:0], Addr 44 (CP), Address 0xED[1:0]; Address 0xF0[7:0] (Read Only)
This readback displays the maximum signal level measured during the active video on channel C.
Function
pkv_chc[9:0]
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9.4 CP OFFSET BLOCK

The offset block consists of three independent adders, one for each channel. Using a_offset[9:0], b_offset[9:0], and
offset value can be added to the data. The actual offset used can come from two different sources:
1. The ADV7850 includes an automatic selection of the offset value, dependent on the CSC mode that is programmed by the user.
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2. A manual, user defined value can be programmed.
When the offset registers (a_offset[9:0], b_offset[9:0], and c_offset[9:0]) contain the value 0x3FF (reset default), the offset used is
determined using the automatic selection process. For any other value in the offset registers, the automatic selection is disabled and the
user-programmed offset value is applied directly to the video. Refer to the flowchart in
Use value from I2C register
OFFSET_A/B/C[9:0] directly
In some applications, it is desirable to use the AGC to gain the signal to a smaller range, then use the Offset block to preserve the
synchronizations (by lifting the whole video signal up), and thus output the full digitized waveform (including synchronizations) within
the 10-bit output range. For this application, the offset values are very important. Refer to the description of
information.
For RGB type output data, the three offset values should be programmed to 0 or 64 (desired code output for black video). For YPbPr type
output data, a_offset[9:0] should be set to 64 (desired code for black); and b_offset[9:0] and c_offset[9:0] (for Pr and Pb) are typically set
to 512 (mid range).
Notes:
• Adding an excessive offset onto the data will result in clipping of the signal.
• The offset value can only be positive; it is an unsigned number.
• ADV7850 employs sequencers for the offset values that prohibit intermediate wrong values to be applied.
Rev. A May 2012
Description
Readback value
Description
Readback value
op_656_range are used to derive offset values.
No
RGB_OUT = 1
Channel
OP_656_RANGE = 1
A 64
64
B
64
C

Figure 81: Channel A, B, and C Automatic Value Selection

I2C Register value
OFFSET_A/B/C[9:0] ==
0x3FF
OFFSET
OP_656_RANGE = 0
OP_656_RANGE = 1
0
0
0
252
Figure 81.
Yes
RGB_OUT = 0
OP_656_RANGE = 0
64
0
512 512
512 512
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ADV7850
c_offset[9:0] a fixed
for additional