Cirrus Logic CS4297A - Manual (Page 32)

CS4297A
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5. POWER MANAGEMENT
5.1 AC ’97 Reset Modes
The CS4297A supports three reset methods, as de-
fined in the AC ’97 Specification: Cold AC ’97 Re-
set, Warm AC ’97 Reset, Register AC ’97 Reset. A
Cold Reset results in all AC ’97 logic (registers in-
cluded) initialized to its default state. A Warm Re-
set leaves the contents of the AC ’97 register set
unaltered. A Register Reset initializes only the
AC ’97 registers to their default states.
5.1.1 Cold AC ‘97 Reset
A Cold Reset is achieved by asserting RESET# for
a minimum of 1 µs after the power supply rails
have stabilized. This is done in accordance with the
minimum timing specifications in the AC ’97 Seri-
al Port Timing section on page 7. Once deasserted,
all of the CS4297A registers will be reset to their
default power-on states and the BIT_CLK and
SDATA_IN signals will be reactivated.
5.1.2 Warm AC ’97 Reset
A Warm Reset allows the AC-link to be reactivated
without losing information in the CS4297A regis-
ters. A Warm Reset is required to resume from a
D3
hot
state, where the AC-link had been halted yet
full power had been maintained. A primary codec
Warm Reset is initiated when the SYNC signal is
driven high for at least 1 µs and then driven low in
the absence of the BIT_CLK clock signal. The
BIT_CLK clock will not restart until at least 2 nor-
mal BIT_CLK clock periods (162.8 ns) after the
SYNC signal is deasserted. A Warm Reset of the
secondary codec is recognized when the primary
codec on the AC-link resumes BIT_CLK genera-
tion. The CS4297A will wait for BIT_CLK to be
stable to restore SDATA_IN activity and/or
S/PDIF transmission on the following frame.
5.1.3 Register AC ’97 Reset
The third reset mode provides a Register Reset to
the CS4297A. This is available only when the
CS4297A AC-link is active and the Codec Ready
bit is ‘set’. The audio (including extended audio)
registers (Index 00h - 38h) and the vendor specific
registers (Index 5Ah - 7Ah) are reset to their default
states by a write of any value to the Reset Register
(Index 00h).
32 DS318PP6
CS4297A