CS4235 Datasheet, PDF (53/94 Pages) Cirrus Logic – CrystalClear Low Cost ISA Audio System

CS4235
CrystalClear ^TM Low Cost ISA Audio System
SOUND BLASTER INTERFACE
The Sound Blaster Pro compatible interface is
the third physical device in logical device 0.
Since the WSS Codec and the Sound Blaster are
mutually exclusive, the WSS Codec interrupt
and playback DMA channel are shared with the
Sound Blaster interface.
Mode Switching
To facilitate switching between different func-
tional modes (i.e. Sound Blaster and Windows
Sound System), logic is included to handle the
switch transparently to the host. No special soft-
ware is required on the host side to perform the
mode switch.
Sound Blaster Direct Register Interface
The Sound Blaster software interface utilizes 10-
bit address decoding and is compatible with
Sound Blaster and Sound Blaster Pro interfaces.
10-bit addressing requires that the upper address
bits be 0 to decode a valid address, i.e. no alias-
ing occurs. This device requires 16 I/O locations
located at the PnP address ’SBbase’. The fol-
lowing registers, shown in Table 14, are
provided for Sound Blaster compatibility.
Left/Right FM Registers,
SBbase+0 - SBbase+3
These registers are mapped directly to the appro-
priate FM synthesizer registers.
Mixer Address Register,
SBbase+4, write only
This register is used to specify the index address
for the mixer. This register must be written be-
fore any data is accessed from the mixer
registers. The mixer indirect register map is
shown in Table 15.
Mixer Data Register,
SBbase+5
This register provides read/write access to a par-
ticular mixer register depending on the index
address specified in the Mixer Address Register.
Address
SBbase+0
SBbase+0
SBbase+1
SBbase+2
SBbase+2
SBbase+3
SBbase+4
SBbase+5
SBbase+6
SBbase+8
SBbase+8
SBbase+9
SBbase+A
SBbase+C
SBbase+C
SBbase+E
Description
Left FM Status Port
Left FM Register Status Port
Left FM Data Port
Right FM Status Port
Right FM Register Status Port
Right FM Status Port
Mixer Register Address
Mixer Data Port
Reset
FM Status Port
FM Register port
FM Data Port
Read Data Port
Command/Write Data
Write Buffer Status (Bit 7)
Data Available Status (Bit 7)
Table 14. Sound Blaster Pro Compatible I/O Interface
Type
Read
Write
Write Only
Read
Write
Write Only
Write Only
Read/Write
Write Only
Read Only
Write
Write Only
Read Only
Write
Read
Read
DS252PP2
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