CS4235 Datasheet, PDF (69/94 Pages) Cirrus Logic – CrystalClear Low Cost ISA Audio System

CS4235
CrystalClear ^TM Low Cost ISA Audio System
Changing Audio Data Formats
In MODE 1, MCE must be used to select the
audio data format in I8. Since MCE causes a
calibration cycle, it is not ideal for full-duplex
operation. In MODE 2 and 3, individual Mode
Change Enable bits for capture and playback are
provided in register I16. MCE (R0) must still be
used to select the sample frequency, but PMCE
(playback) and CMCE (capture) allow changing
the respective data formats without causing a
calibration to occur. Setting PMCE (I16) clears
the playback FIFO and allows the upper four
bits of I8 to be changed. Setting CMCE (I16)
clears the capture FIFO and allows the upper
four bits of I28 to be changed.
Audio Data Formats
The sample frequency is always selected in the
Fs & Playback Data Format register (I8). In
MODE 1 the same register, I8, determines the
audio data format for both playback and capture;
however, in MODE 2 and 3, I8 only selects the
playback data format and the capture data format
is independently selectable in the Capture Data
Format register (I28).
The WSS Codec always orders the left channel
data before the right channel. Note that these
definitions apply regardless of the specific for-
mat of the data. For example, the left sample
always comes first in the data stream regardless
of whether the sample is 16-bit or 8-bit in size.
There are two data formats supported by the
WSS Codec: 16-bit signed (little Endian) and 8-
bit unsigned. See Figures 12-15.
16-BIT SIGNED
The 16-bit signed data format is "little Endian".
This format defines the byte ordering of a multi-
byte word as having the least significant byte
occupying the lowest memory address. Likewise,
the most significant byte of a little Endian word
occupies the highest memory address.
DS252PP2
The 16-bit signed format (also called 16-bit 2’s
complement) is the standard method of repre-
senting 16-bit digital audio. This format gives
96 dB theoretical dynamic range and is the
standard for compact disk audio players. This
format uses the value -32768 (8000h) to repre-
sent maximum negative analog amplitude, 0 for
center scale, and 32767 (7FFFh) to represent
maximum positive analog amplitude.
8-BIT UNSIGNED
The 8-bit unsigned format is commonly used in
the personal computer industry. This format de-
livers a theoretical dynamic range of 48 dB. This
format uses the value 0 (00h) to represent maxi-
mum negative analog amplitude, 128 for center
scale, and 255 (FFh) to represent maximum
positive analog amplitude. The 16-bit signed and
8-bit unsigned transfer functions are shown in
Figure 11.
DMA Registers
The DMA registers allow easy integration of this
part into ISA systems. Peculiarities of the ISA
DMA controller require an external count
mechanism to notify the host CPU of a full
DMA buffer via interrupt. The programmable
DMA Base registers provide this service.
Figure 11. Linear Transfer Functions
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