CS4237B Datasheet, PDF (78/114 Pages) Cirrus Logic – CrystalClear Advanced Audio System with 3D Sound

CS4237B
The third serial format - SPF2, shown in Fig-
ure 11, is called 32-bit mode. This format has 32
SCLKs per frame and FSYNC is high for the
left channel and low for the right channel. The
absolute time is similar to the other two modes
but SCLK is stopped after the right channel is
finished. SCLK is held stopped until the start of
the next frame (stopped for 32 bit period times).
This mode is useful for DSPs that do not want
the interrupt overhead of the 32 unused bit peri-
ods. As an example, if a DSP serial word length
is 16 bits, then four interrupts will occur in SPF0
and SPF1 modes. In mode SPF2 the DSP will
only be interrupted twice.
The fourth serial format - SPF3, shown in Fig-
ure 12, is called ADC/DAC mode. This format
has 64 SCLKs per frame, with FSYNC high
transitions at the start of the left ADC data word
and low transitions at the start of the right ADC
data word. For serial data in, SDIN, both the left
and right 16-bit DAC data word should be fol-
lowed by zeros. For serial data out, SDOUT,
both the left and right ADC data words are fol-
lowed by 16 bits of the DAC data words. The
DAC data words are tapped off the data stream
right before the data enters the Codec DACs (af-
ter all digital summing is done). Having the
ADC and DAC data on the SDOUT allows ex-
ternal modem DSPs to cancel the local audio
source from the local microphone signal.
CS9236 WAVETABLE SERIAL PORT
A digital interface to the Crystal CS9236 Single-
Chip Wavetable Music Synthesizer is provided
that allows the CS9236 PCM audio data to be
summed digitally into the output digital mixer.
The Wavetable Serial port pins are multiplexed
with the XD7-XD5 external bus pins; therefore,
when this serial interface is enabled, any external
peripheral (CDROM, modem, etc.) will need an
external buffer to the ISA bus. This serial port is
enabled via the WTEN bit located in Control
register C8 or in the Global Configuration byte
in the Hardware Configuration data. The hard-
ware connections to the CS9236 are illustrated in
Figure 13.
Volume control for the serial port is supported
through X16 and X17 in the WSS extended reg-
ister space. The volume range is +12 dB to
-82.5 dB with 001000 equal to 0 dB. After vol-
ume is applied to the PCM data, it is summed
into the digital mixer which is then summed into
the analog output mixer.
FSYNC
SCLK
SDIN
SDOUT
...
...
15 14 13 ^... 0
15 14 13 ^... 0
15
DAC 16 Clocks
DAC 16 Clocks
15 14 13 ^... 0 15 14 13 ^... 0 15 14 13 ^... 0 15 14 13 ^... 0 15
ADC 16 Clocks DAC 16 Clocks
Left Data
ADC 16 Clocks DAC 16 Clocks
Right Data
Figure 12. ADC/DAC Mode (SF1,0 = 11)
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