ADV7181B
Rev. B | Page 31 of 100
For example, program the ADV7181B into manual fixed gain
mode with a desired gain of 0.89.
1.
Use Equation 1 to convert the gain:
0.89 × 2048 = 1822.72
2.
Truncate to integer value:
1822.72 = 1822
3.
Convert to hexadecimal:
1822d = 0x71E
4.
Split into two registers and program:
Luma Gain Control 1[3:0] = 0x7
Luma Gain Control 2[7:0] = 0x1E
5.
Enable manual fixed gain mode:
Set LAGC[2:0] to 000
BETCAM Enable Betacam Levels, Address 0x01[5]
If YPrPb data is routed through the ADV7181B, the automatic
gain control modes can target different video input levels, as
outlined in Table 39. The BETACAM bit is valid only if the
input mode is YPrPb (component). The BETACAM bit
basically sets the target value for AGC operation.
A review of the following sections is useful:
•
SETADC_sw_man_en, Manual Input Muxing Enable,
Address C4[7] to find how component video (YPrPb) can
be routed through the ADV7181B.
•
Video Standard Selection to select the various standards,
for example, with and without pedestal.
The automatic gain control (AGC) algorithms adjust the levels
based on the setting of the BETACAM bit (see Table 36).
Table 36. BETACAM Function
BETACAM Description
0 (default)
Assuming YPrPb is selected as input format
Selecting PAL with pedestal selects MII
Selecting PAL without pedestal selects SMPTE
Selecting NTSC with pedestal selects MII
Selecting NTSC without pedestal selects SMPTE
1
Assuming YPrPb is selected as input format
Selecting PAL with pedestal selects BETACAM
Selecting PAL without pedestal selects BETACAM
variant
Selecting NTSC with pedestal selects BETACAM
Selecting NTSC without pedestal selects BETACAM
variant
PW_UPD Peak White Update, Address 0x2B[0]
The peak white and average video algorithms determine the
gain based on measurements taken from the active video. The
PW_UPD bit determines the rate of gain change. LAGC[2:0]
must be set to the appropriate mode to enable the peak white or
average video mode in the first place. For more information,
refer to the LAGC[2:0] Luma Automatic Gain Control,
Address 0x2C[7:0] section.
Setting PW_UPD to 0 updates the gain once per video line.
Setting PW_UPD to 1 (default) updates the gain once per field.
Chroma Gain
CAGC[1:0] Chroma Automatic Gain Control,
Address 0x2C[1:0]
The two bits of color automatic gain control mode select the
basic mode of operation for automatic gain control in the
chroma path.
Table 37. CAGC Function
CAGC[1:0] Description
00
Manual fixed gain (use CMG[11:0])
01
Use luma gain for chroma
10 (default)
Automatic gain (based on color burst)
11 Freeze
chroma
gain
CAGT[1:0] Chroma Automatic Gain Timing,
Address 0x2D[7:6]
The chroma automatic gain timing register allows the user to
influence the tracking speed of the chroma automatic gain
control. This register has an effect only if the CAGC[1:0]
register is set to 10 (automatic gain).
Table 38. CAGT Function
CAGT[1:0] Description
00
Slow (TC = 2 sec)
01
Medium (TC = 1 sec)
10
Fast (TC = 0.2 sec)
11 (default)
Adaptive
Table 39. Betacam Levels
Name
Betacam (mV)
Betacam Variant (mV)
SMPTE (mV)
MII (mV)
Y Range
0 to 714 (includes 7.5% pedestal)
0 to 714
0 to 700
0 to 700 (includes 7.5% pedestal)
Pb and Pr Range
–467 to +467
–505 to +505
–350 to +350
–324 to +324
Sync Depth
286
286
300
300
