Wolfson WM8978, Manual, Page: 100 / 119

WM8978
Production Data
w
PD, Rev 4.5, October 2011
100
REGISTER
ADDRESS
BIT LABEL DEFAULT DESCRIPTION REFER TO
2:0 ALCMINGAIN 000 Set minimum gain of PGA
000=-12dB
001=-6dB
010=0dB
011=+6dB
100=+12dB
101=+18dB
110=+24dB
111=+30dB Input Limiter/
Automatic
Level Control
(ALC)
33 (21h) 8 0 Reserved
7:4 ALCHLD 0000 ALC hold time before gain is increased.
0000 = 0ms
0001 = 2.67ms
0010 = 5.33ms
… (time doubles with every step)
1010 or higher = 1.36s Input Limiter/
Automatic
Level Control
(ALC)
3:0 ALCLVL 1011 ALC target – sets signal level at ADC input
1111 : -1.5dBFS
1110 : -1.5dBFS
1101 : -3dBFS
1100 : -4.5dB management...... (-1.5dB steps)
0001 : -21dBFS
0000 : -22.5dBFS Input Limiter/
Automatic
Level Control
(ALC)
34 (22h) 8 ALCMODE 0 Determines the ALC mode of operation:
0=ALC mode
1=Limiter mode Input Limiter/
Automatic
Level Control
(ALC)
7:4 ALCDCY
[3:0]
0011 Decay (gain ramp-up) time
(ALCMODE ==0) Input Limiter/
Automatic
Level Control
(ALC)
Per step Per 6dB 90% of range
0000 410us 3.28ms 23.6ms
0001 820us 6.56ms 47.2ms
0010 1.64ms 13.1ms 94.5ms
… (time doubles with every step)
1010
or
higher
420ms 3.36s 24.2s
0011 Decay (gain ramp-up) time
(ALCMODE ==1)
Per step Per 6dB 90% of range
0000 90.8us 726us 5.23ms
0001 182us 1.45ms 10.5ms
0010 363us 2.91ms 20.9ms
… (time doubles with every step)
1010 93ms 744ms 5.36s
3:0 ALCATK 0010 ALC attack (gain ramp-down) time
(ALCMODE == 0) Input Limiter/
Automatic
Level Control
(ALC)
Per step Per 6dB 90% of range
0000 104us 832us 6ms
0001 208us 1.66ms 12ms
0010 416us 3.33ms 24ms
… (time doubles with every step)