CS4235 Datasheet, PDF (68/94 Pages) Cirrus Logic – CrystalClear Low Cost ISA Audio System

CS4235
CrystalClear ^TM Low Cost ISA Audio System
brated in this mode, any signals fed through the
mixer will be unaffected. The calibration se-
quence is as follows:
The DACs are muted
The ADCs are calibrated
The DACs are calibrated
The DACs are unmuted
DAC CALIBRATION (CAL1,0 = 10)
This calibration mode only clears the DACs
(playback) interpolation filters leaving the ADC
unaffected. This is the second fastest calibration
mode (no cal. is the fastest) taking 120 sample
periods at 44.1 kHz to complete. The calibration
sequence is as follows:
The DACs are muted
The DAC filters are cleared
The DACs are unmuted
FULL CALIBRATION (CAL1, 0 = 11)
This calibration mode calibrates all offsets,
ADCs, DACs, and analog mixers. Full calibra-
tion will automatically be initiated on power up
or anytime the WSS Codec exits from a full
power down state. This is the longest calibration
mode and takes 450 sample periods at 44.1 kHz
to complete. The calibration sequence is as fol-
lows:
All outputs are muted (DACs and mixer)
The mixer is calibrated
The ADCs are calibrated
The DACs are calibrated
All outputs are unmuted
Changing Sampling Rate
The internal states of the WSS Codec are syn-
chronized by the selected sampling frequency.
The sample frequency can be set in one of three
fashions. The standard WSS Codec method uses
the Fs & Playback Data Format register (I8) to
set the sample frequency. The changing of either
the clock source or the clock frequency divide
requires a special sequence for proper WSS
Codec operation:
1) Place the WSS Codec in Mode Change En-
able using the MCE bit of the Index Address
register (R0).
2) During a single write cycle, change the Clock
Frequency Divide Select (CFS) and/or
Clock 2 Base Select (C2SL) bits of the Fs &
Playback Data Format register (I8) to the de-
sired value. (The data format may also be
changed.)
3) The WSS Codec resynchronizes its internal
states to the new frequency. During this time
the WSS Codec will be unable to respond.
Writes to the WSS Codec will not be recog-
nized and reads will always return the value
80 hex.
4) The host now polls the WSS Codec’s Index
Address register (R0) until the value 80 hex
is no longer returned. On slow processor sys-
tems, 80h may go away faster than read
from software (the software would never see
it).
5) Once the WSS Codec is no longer responding
to reads with a value of 80 hex, normal op-
eration can resume and the WSS Codec can
be removed from MCE.
A second method of changing the sample fre-
quency is to disable the sample frequency bits in
I8 (lower four bits) by setting SRE in I22. When
this bit is set, OSM1 and OSM0 in I10, along
with the rest of the bits in I22, are used to set the
sample frequency. Once enabled, these bits can
be changed without doing an MCE cycle.
The third method supports independent sample
frequencies (Fs) for capture and playback. The
independent sample frequency mode is enabled
by setting IFSE in X11. Once enabled, the other
two methods for setting Fs (I8, I10, and I22) are
disabled. The capture (ADC) Fs is set in X12
and the playback (DAC) Fs is set in X13.
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