Production Data
WM8912
CONTROL WRITE SEQUENCER
The Control Write Sequencer is a programmable unit that forms part of the WM8912 control interface
logic. It provides the ability to perform a sequence of register write operations with the minimum of
demands on the host processor - the sequence may be initiated by a single operation from the host
processor and then left to execute independently.
Default sequences for Start-Up and Shutdown are provided (see “Default Sequences” section). It is
recommended that these default sequences are used unless changes become necessary.
When a sequence is initiated, the sequencer performs a series of pre-defined register writes. The
host processor informs the sequencer of the start index of the required sequence within the
sequencer’s memory. At each step of the sequence, the contents of the selected register fields are
read from the sequencer’s memory and copied into the WM8912 control registers. This continues
sequentially through the sequencer’s memory until an “End of Sequence” bit is encountered; at this
point, the sequencer stops and an Interrupt status flag is asserted. For cases where the timing of the
write sequence is important, a programmable delay can be set for specific steps within the sequence.
Note that the Control Write Sequencer’s internal clock is derived from the internal clock SYSCLK. An
external MCLK signal must be present when using the Control Write Sequencer, and SYSCLK must
be enabled by setting CLK_SYS_ENA (see “Clocking and Sample Rates”). The clock division from
MCLK is handled transparently by the WM8912 without user intervention, as long as MCLK and
sample rates are set correctly.
INITIATING A SEQUENCE
The Register fields associated with running the Control Write Sequencer are described in Table 56.
The Write Sequencer Clock is enabled by setting the WSEQ_ENA bit. Note that the operation of the
Control Write Sequencer also requires the internal clock SYSCLK to be enabled via the
CLK_SYS_ENA (see “Clocking and Sample Rates”).
The start index of the required sequence must be written to the WSEQ_START_INDEX field. Setting
the WSEQ_START bit initiates the sequencer at the given start index.
The Write Sequencer can be interrupted by writing a logic 1 to the WSEQ_ABORT bit.
The current status of the Write Sequencer can be read using two further register fields - when the
WSEQ_BUSY bit is asserted, this indicates that the Write Sequencer is busy. Note that, whilst the
Control Write Sequencer is running a sequence (indicated by the WSEQ_BUSY bit), normal
read/write operations to the Control Registers cannot be supported. (The Write Sequencer registers
and the Software Reset register can still be accessed when the Sequencer is busy.) The index of the
current step in the Write Sequencer can be read from the WSEQ_CURRENT_INDEX field; this is an
indicator of the sequencer’s progress. On completion of a sequence, this field holds the index of the
last step within the last commanded sequence.
When the Write Sequencer reaches the end of a sequence, it asserts the WSEQ_EINT flag in
Register R127 (see Table 54 within the “Interrupts” section). This flag can be used to generate an
Interrupt Event on completion of the sequence. Note that the WSEQ_EINT flag is asserted to
indicate that the Write Sequencer is NOT Busy.
REGISTER
ADDRESS
BIT
LABEL
DEFAULT
DESCRIPTION
R108 (6Ch)
8
WSEQ_ENA
0
Write Sequencer Enable.
0 = Disabled
Write
Sequencer 0
1 = Enabled
R111 (6Fh)
9
WSEQ_ABORT
0
Writing a 1 to this bit aborts the
current sequence and returns
control of the device back to the
serial control interface.
Write
Sequencer 3
PD, Rev 4.0, September 2010
83
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WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
