CS4237B Datasheet, PDF (76/114 Pages) Cirrus Logic – CrystalClear Advanced Audio System with 3D Sound

CS4237B
Modem Interface
The modem interface, Logical Device 5 (LD5)
consist of:
MCS - Modem Chip Select
MINT - Modem Interrupt
The other signals such as address bits, data
strobes, data, and reset are provided by the Ex-
ternal Peripheral Port. The interface allows the
host computer to access up to eight I/O mapped
locations.
The Modem signals are multiplexed with both
the upper ISA address pins, and the CDROM
DMA pins. To enable the Modem, first a pull-
down resistor must be placed on XIOR which
disables the upper ISA address pins. Second, the
Modem base address, COMbase, must be pro-
grammed to a non-zero value which will convert
the SA13/CDACK/MCS pin to the modem chip
select MCS, and the SA15/CDRQ/MINT pin to
the modem interrupt pin MINT. Once these two
pins switch to modem pins, they can only be
changed by resetting the part. COMbase, Logical
Device 5 base address 0, is programmed via PnP
or the SLAM method.
The polarity of MINT is programmable via
Hardware Configuration data, IHM in byte 7, or
through CTRLbase+1. The default is active low
(IHM = 0).
DSP SERIAL AUDIO DATA PORT
The WSS Codec includes a DSP serial audio in-
terface for transferring digital audio data
between the part and an external serial device
such as a DSP processor. The DSP serial port
pins are multiplexed with either the #2 joystick
inputs of the Game Port interface or a portion of
the XD peripheral bus. The selection is made via
the SPS bit located in Control register C8, or the
Global Config. byte in the Hardware Configura-
tion data. If SPS is 0, the joystick B pins convert
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to the DSP serial port when SPE is set (MCE
must be 1 to change SPE). If SPS is 1, XD<4:1>
convert to the DSP serial port when SPE is set.
In this case, SD<7:0> is disabled on reads of pe-
ripheral port addresses (CDROM, modem, etc.)
since XD<7:0> is no longer available.
The DSP audio serial port is software enabled
via the SPE bit in the WSS Codec indirect regis-
ter I16. The ISA interface is fully active in this
mode. While the serial port is enabled, audio
data may still be read from the ADCs over the
ISA bus, and the DACs will sum data from the
SDIN pin, the parallel ISA bus data, and the in-
ternal FM synthesizer engine. The serial port
sample frequency is always 44.1 kHz regardless
of the ISA bus sample frequency, and the data
format is always two’s complement 16-bit linear.
FSYNC and SCLK are always output from the
part when the serial port is enabled. The serial
port can be configured in one of four serial port
formats, shown in Figures 9-12. SF1 and SF0 in
I16 select the particular format. MCE in R0 must
be set to change SF1/0. Both left and right audio
words are always 16 bit two’s complement.
When the mono audio format is selected, the
right channel output is set to zero and the left
channel input is summed to both DAC channels.
The first format - SPF0, shown in Figure 9, is
called 64-bit enhanced. This format has 64
SCLKs per frame with a one bit period wide
FSYNC that precedes the frame. The first 16 bits
occupy the left word and the second 16 bits oc-
cupy the right word. The last 32 bits contain four
status bits and 28 zeros. This is the only mode
that contains status information.
The second serial format - SPF1, shown in Fig-
ure 10, is called 64-bit mode. This format has 64
SCLKs per frame, with FSYNC high transitions
at the start of the left data word and low transi-
tions at the start of the right data word. Both the
left and right data words are followed by 16 ze-
ros.
DS213PP4