Manual Gain Control; Figure 80: Cp Automatic Gain Controls - Analog Devices ADV7850 Hardware Manual

• Manual Gain Configuration
This configuration is enabled by setting
processed by the CP core is configured via the control registers a_gain[9:0],
Automatic Gain Control Configuration
•
This configuration is enabled by setting
and Polarity Detector (SSPD), is used to determine automatically the presence of external digital synchronizations, for example,
HSync/VSync, or embedded synchronization. The detection result of the SSPD block is used to enable/disable the automatic
gain control mode.
If SSPD detects the presence of external (that is, digital) synchronization signals, the gain block in the CP core is controlled by
op_656_range because it is assumed that there is no embedded synchronization present and it is, therefore, not possible to adjust
the gain automatically.
• If the SSPD does not find any external synchronization signal, it concludes that the synchronization must be embedded. This
switches the gain block in the CP core into automatic mode (refer to Section 9.7). This function can be disabled using the AGC
mode manual enable control, agc_mode_man, as illustrated in
OP_656_RANGE
0 (0-255 Output)
(255-0+1)x16/1344 = 3.047
1 (16-235 Y/RGB,
(235-16+1)x16/1344 = 2.617
16-240 CrCb)
agc_mode_man, Addr 44 (CP), Address 0x73[6]
This control is used to set how the gain for all three channels is configured.
Function
agc_mode_man
0 
1

Manual Gain Control

9.3.4
The automatic gain control (AGC) can be completely disabled by setting the gain control block into a manual mode. By setting the
gain_man bit, the gain factors for channels A, B, and C are no longer taken from the AGC, but are replaced by three dedicated I
registers.
Using these factors with the hsd_fb[9:0] register, it is possible to implement an off-chip AGC if desired. The range for the gain is
[0...3.999]. The registers a_gain[9:0], b_gain[9:0], and c_gain are in 2.8 binary format and can be set as shown in
where:
≤ GAIN
0
Rev. A May 2012
agc_mode_man
agc_mode_man
No
AGC_MODE_MAN
GAIN

Figure 80: CP Automatic Gain Controls

Description
Gain dependant on type of input and op_656_range
Gain operation controlled by gain_man
x
<
4
to 1 and gain_man
to 1 and gain_man
Figure 80.
Yes
GAIN_MAN
Yes
Set gain based on
A/B/C_GAIN[9:0]
values
AGC
Active
(
= ×
_ gain [ : 9 ] 0 floor GAIN
245
to 1. In this case the gain applied to the video data
b_gain[9:0] and c_gain[9:0].
to 0. The detection block, Synchronization Source
No
No
Yes
SSPD detected
embedded syncs?
OP_656_RANGE
0 (0-255 Output)
1 (16-235 Y/RGB,
16-240 CrCb)
)
256
ADV7850
GAIN
(255-0+1)x16/1344 = 3.047
(235-16+1)x16/1344 = 2.617
C
2
Equation 10.