CS4239 Datasheet, PDF (71/98 Pages) Cirrus Logic – CrystalClear™ Portable ISA Audio System

CS4239
CrystalClear^TM Portable ISA Audio System
There are two data formats supported by the
WSS Codec: 16-bit signed (little Endian) and 8-
bit unsigned. See Figures 13-16.
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.
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 12.
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.
The act of writing a value to the Upper Base
register causes both Base registers to load the
Current Count register. DMA transfers are en-
abled by setting the PEN/CEN bit while
DS253PP2
PPIO/CPIO is clear. (PPIO/CPIO can only be
changed while the MCE bit is set.) Once trans-
fers are enabled, each sample that is transferred
by a DMA cycle will decrement the Current
Count register until zero is reached. The next
sample after zero generates an interrupt and re-
loads the Current Count registers with the values
in the Base registers.
For all data formats the DMA Base registers
must be loaded with the number of samples, mi-
nus one, to be transferred between "DMA
Interrupts". A sample is one to four bytes wide
and is defined as all data taken at one instant in
time. Stereo and mono data contain the same
number of samples, and 8-bit data and 16-bit
data contain the same number of samples.
Symbolically:
DMA Base register₁₆ = N_S - 1
Where N_S is the number of samples transferred
between interrupts and the "DMA Base regis-
ter₁₆" consists of the concatenation of the upper
and lower DMA Base registers.
Figure 12. Linear Transfer Functions
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