
ADAU1781
Rev. B| Page 27 of 92
CLOCKING AND SAMPLING RATES
f/X
INPUT DIVIDE
1, 2, 3, 4
f × (R + N/M)
INTEGER, NUMERATOR,
DENOMINATOR
INPUT MASTER
CLOCK FREQUENCY
256 ×
fS, 512 × fS,
768 ×
fS, 1024 × fS
MCKI
PLL CONTROL
CLOCK CONTROL
AUTOMATICALLY SET TO 1024 ×
fS
WHEN PLL CLOCK SOURCE SELECTED
ADCs
DACs
fS/
0.5, 1, 1.5, 2, 3, 4, 6
SOUND ENGINE
FRAME RATE
SOUND
ENGINE
fS/
0.5, 1, 1.5, 2, 3, 4, 6
CONVERTER
SAMPLING RATE
fS/
0.5, 1, 1.5, 2, 3, 4, 6
SERIAL PORT
SAMPLING RATE
SERIAL DATA
INPUT/OUTPUT
PORTS
ADC_S
D
AT
A
/GP
IO1
B
C
LK
/GP
IO2
LR
C
LK
/GP
IO3
DAC_S
D
AT
A
/GP
IO0
CORE
CLOCK
08314-
027
Figure 28. Clock Routing Diagram
CORE CLOCK
The core clock divider generates a core clock either from the
PLL or directly from MCLK and can be set in Register 16384
(0x4000), clock control.
The core clock is always in 256 × fS mode. Direct MCLK fre-
quencies must correspond to a value listed in Table 12, where fS is the base sampling frequency. PLL outputs are always in 1024
× fS mode, and the clock control register automatically sets the
core clock divider to f/4 when using the PLL.
Table 12. Core Clock Frequency Dividers
Input Clock Rate
Core Clock Divider
Core Clock
256 × f
S
f/1
256 × f
S
512 × f
S
f/2
768 × f
S
f/3
1024 × f
S
f/4
Clocks for the converters, the serial ports, and the SigmaDSP
core are derived from the core clock. The core clock can be
derived directly from MCLK, or it can be generated by the
PLL. Register 16384 (0x4000), clock control, Bit 3, clock source
select, determines the clock source.
Bits[2:1], input master clock frequency, should be set according
to the expected input clock rate selected by Bit 3, clock source
select. The clock source select value also determines the core
clock rate and the base sampling frequency, fS.
For example, if the input to Bit 3 = 49.152 MHz (from PLL),
then Bits[2:1] = 1024 × fS; therefore,
fS = 49.152 MHz/1024 = 48 kHz
Table 13. Clock Control Register (Register 16384, 0x4000)
Bits
Bit Name
Settings
3
Clock source select
0: direct from MCKI pin (default)
1: PLL clock
[2:1]
Input master clock
frequency
00: 256 × f
S (default)
01: 512 × f
S
10: 768 × f
S
11: 1024 × f
S
0
Core clock enable
0: core clock disabled (default)
1: core clock enabled
SAMPLING RATES
The ADCs, DACs, and serial port share a common sampling
rate that is set in Register 16407 (0x4017), Converter Control 0.
Bits[2:0], converter sampling rate, set the sampling rate as a ratio of
the base sampling frequency. The SigmaDSP core sampling rate
is set in Register 16619 (0x40EB), SigmaDSP core frame rate,
Bits[3:0], SigmaDSP core frame rate, and the serial port
sampling rate is set in Register 16632 (0x40F8), serial port
sampling rate, Bits[2:0], serial port control sampling rate.
It is strongly recommended that the sampling rates for the
converters, serial ports, and SigmaDSP core be set to the same
value, unless appropriate compensation filtering is done within
the SigmaDSP core.