CS4237B Datasheet, PDF (27/114 Pages) Cirrus Logic – CrystalClear Advanced Audio System with 3D Sound

CS4237B
MODE 1. Except for the Capture Data Format
(I28), Capture Base Count (I30/31), and Alter-
nate Feature Status (I24) registers, all other
Mode 2 functions retain their values when re-
turning to Mode 1. The WSS Codec is
backwards compatible with the CS4236,
CS4232, CS4231 and CS4248.
The additional MODE 2 functions are: full-du-
plex support, a programmable timer, Mono In
and Mono Out support.
MODE 3 is selected by setting CMS1,0 to 11.
MODE 3 allows access to new bits in the indi-
rect registers I0-I31, and allows access to a third
set of "extended registers" which are designated
X0-X17+X25. The extended registers are ac-
cessed through I23. The additional MODE 3
functions are:
1. A full symmetrical mixer. This changes the in-
put multiplexer to a input mixer.
2. Independent sample frequency control on the
ADCs and DACs.
3. Programmable Gain and Attenuation on the
Microphone inputs.
4. Independent control over the volume of inter-
nal FM synthesis and external wavetable.
5. Volume control on the DSP serial port input
data.
6. Stereo volume on the monitor feedback path.
FIFOs
The WSS Codec contains 16-sample FIFOs in
both the playback and capture digital audio data
paths. The FIFOs are transparent and have no
programming associated with them.
When playback is enabled, the playback FIFO
continually requests data until the FIFO is full,
and then makes requests as positions inside the
FIFO are emptied, thereby keeping the playback
FIFO as full as possible. Thus when the system
cannot respond within a sample period, the FIFO
starts to empty, avoiding a momentary loss of
audio data. If the FIFO runs out of data, the last
valid sample can be continuously output to the
DACs (if DACZ in I16 is set) which will elimi-
nate pops from occurring.
When capture is enabled, the capture FIFO tries
to continually stay empty by making requests
every sample period. Thus when the system can-
not respond within a sample period, the capture
FIFO starts filling, thereby avoiding a loss of
data in the audio data stream.
WSS Codec PIO Register Interface
Four I/O mapped locations are available for ac-
cessing the Codec functions and mixer. The
control registers allow access to status, audio
data, and all indirect registers via the index reg-
isters. The IOR and IOW signals are used to
define the read and write cycles respectively. A
PIO access to the Codec begins when the host
puts an address on to the ISA bus which matches
WSSbase and drives AEN low. WSSbase is pro-
grammed during a Plug and Play configuration
sequence. Once a valid base address has been
decoded then the assertion of IOR will cause the
WSS Codec to drive data on the ISA data bus
lines. Write cycles require the host to assert data
on the ISA data bus lines and strobe the IOW
signal. The WSS Codec will latch data into the
PIO register on the rising edge of the IOW
strobe.
The audio data interface typically uses DMA re-
quest/grant pins to transfer the digital audio data
between the WSS Codec and the bus. The WSS
Codec is responsible for asserting a request sig-
nal whenever the Codec’s internal buffers need
updating. The bus responds with an acknowledge
signal and strobes data to and from the Codec, 8
bits at a time. The WSS Codec keeps the request
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