CS4205_05 Datasheet, PDF (60/81 Pages) Cirrus Logic – CrystalClear® Audio Codec ’97 for Portable Computing

CS4205
10.2 Powerdown Controls
The Powerdown Control/Status Register
(Index 26h) controls the power management func-
tions. The PR[5:0] bits in this register control the
internal powerdown states of the CS4205. Power-
down control is available for individual subsections
of the CS4205 by asserting any PRx bit or any com-
bination of PRx bits. All powerdown states except
PR4 and PR5 can be resumed by clearing the cor-
responding PRx bit. Table 24 shows the mapping
of the power control bits to the functions they man-
age.
When PR0 is ‘set’, the L/R ADCs and the Input
Mux are shut down and the ADC bit in the Power-
down Control/Status Register (Index 26h) is
‘cleared’ indicating the ADCs are no longer in a
ready state. The same is true for PR1 and the
DACs, PR2 and the analog mixer, and PR3 and the
voltage reference (Vrefout). When one of these bits
is ‘cleared’, the corresponding subsystem will be-
gin a power-on process, and the associated status
bit will be ‘set’ when the hardware is ready.
In a primary codec the PR4 bit powers down the
AC-link, but all other analog and digital sub-
systems continue to function. The required resume
sequence from a PR4 state is either a Warm Reset
or a New Warm Reset, depending on whether a
D3_hot or D3_cold state has been entered.
The PR5 bit disables all internal clocks and powers
down the DACs and the ADCs, but maintains oper-
ation of the BIT_CLK and the analog mixer. A
Cold Reset is the only way to restore operation to
the CS4205 after asserting PR5. To achieve a com-
plete digital powerdown, PR4 and PR5 must be as-
serted within a single AC output frame. This will
also drive BIT_CLK ‘low’.
The CS4205 does not automatically mute any input
or output when the powerdown bits are ‘set’. The
software driver controlling the AC ’97 device must
manage muting the input and output analog signals
before putting the part into any power management
state. The definition of each PRx bit may affect a
single subsection or a combination of subsections
within the CS4205. Table 25 contains the matrix of
subsections affected by the respective PRx func-
tion. Table 26 shows the different operating power
consumptions levels for different powerdown func-
tions.
PR Bit
Function
PR0
L/R ADCs and Input Mux Powerdown
PR1
Front DACs Powerdown
PR2
Analog Mixer Powerdown (Vref on)
PR3
Analog Mixer Powerdown (Vref off)
PR4
AC-link Powerdown (BIT_CLK off)*
PR5
Internal Clock Disable
* Applies only to primary codec
Table 24. Powerdown PR Bit Functions
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