CS4281
CrystalClear™ PCI Audio Interface
CPU
North
Bridge
Host
Memory
PCI Bus
CS4281
South
Bridge
PCI Audio Interface
Audio Out
AC-Link
CS4298
Audio In
PC/PCI
(if used)
DAA
Telephone
Line
Figure 7. Modem Scenario
HOST INTERFACE
The CS4281 host interface is comprised of two separate interface blocks which are memory mapped into
host address space. The interface blocks can be located anywhere in the host 32-bit physical address space.
The interface block locations are defined by the addresses programmed into the two Base Address Regis-
ters in the PCI Configuration Space. These base addresses are normally set up by the system’s Plug and
Play BIOS. The first interface block (Base Address 0) contains the general purpose configuration, control,
and status registers for the device. The second interface block (Base Address 1) maps the FIFO RAMs into
host memory space. The relationship between the Base Address Registers in the CS4281 PCI Configura-
tion Space and the host memory map is depicted in Figure 8. The bus mastering PCI bus interface complies
with the PCI Local Bus Specification (version 2.1).
Device PCI Config. Space
00h
04h
08h
0Ch
10h
14h
Device ID / Vendor ID
Status / Command
Class Code / Revision
Misc. Control
Base Address Register 0
Base Address Register 1
Direct Memory Interface
(Memory Mapped, 64 kByte)
Direct Registers
(Memory Mapped, 4 kByte)
Figure 8. Host Interface Base Address Registers
CIRRUS LOGIC PRODUCT DATA SHEET
DS308PP4
11
CIRRUS [ CIRRUS LOGIC ]
