Functional description STw5095
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Data is exchanged with MSB first and left channel data first in all formats. Data word-length
is selected with bits DAWL in CR26 and ADWL in CR27. AD_D ATA pin, outside the selected
time slot, is in the impedance condition selected by bit ADHIZ in CR28 in all data formats
except Right-Aligned-Format.
In the following paragraphs SYNC, CK and DATA will be used when the distinction between
AD and DA is not relevant. When Master Mode is selected (bits DAMAST and ADMAST in
CR22 and CR25 respectiv ely) the SYNC and CK clocks are generated internally. In addition,
an oversampled clock can be generated for each interface (AD_OCK and DA_OCK). The
OCK clock is available in Slave Mode also, if needed.
The AD and DA interf aces can also be used as a single bidirectional interface when they are
configured with the same format (Delay ed, DSP, etc.) and AD_SYNC is connected to
DA_SYNC and DA_CK to AD_CK. Master Mode is still available selecting ADMAST or
DAMAST (not both).
The interfaces features are controlled with control registers CR26, CR27 and CR28.
Supported operating formats:
●Delayed-Format (I2S compatible) (DAFORM or ADFORM =000): the Audio Interface
is I2S compatible (
Figure 9 on page 47
). The number of CK periods within one SYNC
period is not relevant, as long as enough CK periods are used to transfer the data and
the maximum frequency limit specified for bit clock is not e xceeded. CK can be either a
continuous clock or a sequence of bursts. In master mode there are 32 CK periods per
SYNC period (that means 16 CK periods per channel) when the word length is 16 bit,
while there are 64 CK periods per SYNC period (or 32 CK periods per channel) when
word length is 18bit or higher. Bits ADSYNCP, DASYNCP and ADCKP, DACKP affect
the interface format inverting the polarity of SYNC and CK pins respectively.
●Left-Aligned-Format (DAFORM or ADFORM =001): this format is equivalent to
Delay ed-Format without the 1 bit clock dela y at the beginning of each frame (
Figure 9
on page 47
).
●Right-Aligned-Format (DAFORM or ADFORM =010): this format is equivalent to
Delayed-Format, except that the Audio Data is right aligned and that the number of CK
periods i s fixed to 64 for each SYNC period (
Figure 9 on page 47
).
●DSP-Format (DAFORM or ADFORM =011) in this format the Audio Interface starting
from a frame sync pulse on SYNC receives (DA) or sends (AD) the Left and Right data
one after the other (
Figure 10 on page 48
). The number of CK periods within one
SYNC period is not relevant, as long as enough CK periods are used to transfer the
data and the maximum frequency limit specified for bit clock is not exceeded. CK can
be either a continuous clock or a sequence of bursts. In Master Mode there are 32 CK
periods per SYNC period when the word length is 16 bit, while there are 64 CK periods
per SYNC period when word length is 18bit or higher. Bit CKP (ADCKP and DACKP)
affects the interf ace format inv erting the polarity of CK pin. Bit SYNCP (ADSYNCP and
DASYNCP) switches between delayed (SYNCP=0) and non delayed (SYNCP=1)
formats.
DSP-Format is suited to interface with a Multi-Channel Serial Port.
●SPI-Format (D AFORM or ADFORM =100) in this f ormat Left and Right data is received
with separate data burst. Every burst is identified with a low level on SYNC signal
(
Figure 10 on page 48
). There is no timing difference between the Left and Right data
burst: the two channels are identified by the startup order: the first burst after AD path
or D A path power-up identifies the Left channel data, the second one is the Right
channel data, then Left and Right data repeat one after the other. CK must have 16
periods per channel in case of 16 bit data word and 32 periods per channel in case of