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82801AA and 82801AB Datasheet
13-5
AC ’97 Modem Controller Registers (D31:F6)
13.1.10
MMBAR—Modem Mixer Base Address Register
(Modem—D31:F6)
Address Offset:
Default Value:
10h
–
13h
00000001h
Attribute:
Size:
R/W
32 bits
The Native PCI Mode Modem uses PCI Base Address register #1 to request a contiguous block of
I/O space that is to be used for the Modem Mixer software interface. The mixer requires 256 bytes
of I/O space. All accesses to the mixer registers are forwarded over the AC-link to the codec where
the registers reside.
In the case of the split codec implementation accesses to the different codecs are differentiated by
the controller by using address offsets 00h
–
7Fh for the primary codec and address offsets 80h
–
FEh
for the secondary codec.
13.1.11
MBAR—Modem Base Address Register (Modem—D31:F6)
Address Offset:
Default Value:
14h
–
17h
00000001h
Attribute:
Size:
R/W
32 bits
The Modem function uses PCI Base Address register #1 to request a contiguous block of I/O space
that is to be used for the Modem software interface. The Modem Bus Mastering register space
requires 128 bytes of I/O space. All Modem registers reside in the controller; therefore, cycles are
NOT forwarded over the AC-link to the codec.
Bit
Description
31:16
Hardwired to 0’s
15:8
Base Address.
These bits are used in the I/O space decode of the Modem interface registers. The
number of upper bits that a device actually implements depends on how much of the address space
the device will respond to. For the AC ‘97 Modem, the upper 16 bits are hardwired to 0, while bits
15:8 are programmable. This configuration yields a maximum I/O block size of 256 bytes for this
base address.
7:1
Reserved. Read as 0
0
Resource Type Indicator (RTE).
This bit is set to one, indicating a request for I/O space.
Bit
Description
31:16
Hardwired to 0’s
15:7
Base Address.
These bits are used in the I/O space decode of the Modem interface registers. The
number of upper bits that a device actually implements depends on how much of the address space
the device will respond to. For the AC ‘97 Modem, the upper 16 bits are hardwired to 0, while bits
15:7 are programmable. This configuration yields a maximum I/O block size of 128 bytes for this
base address.
6:1
Reserved. Read as 0
0
Resource Type Indicator (RTE).
This bit is set to one, indicating a request for I/O space.