Functional Description
5-140
Intel
82801BA ICH2 Datasheet
Input Slot 6: Optional Dedicated Microphone Record Data
Input slot 6 is a third PCM system input channel available for dedicated use by a microphone. This
input channel supplements a true stereo output that enables more precise echo cancellation
algorithm for speakerphone applications. The ICH2 supports 16 bit resolution for slot 6 input.
Input Slots 7-11: Reserved
Input frame slots 7–11 are reserved for future use and should be stuffed with zeros by the codec,
per the AC’97 specification.
Input Slot 12: I/O status
The status of the GPIOs configured as inputs are to be returned on this slot in every frame. The data
returned on the latest frame is accessible to software by reading the register at offset 54h/D4h in the
codec I/O space. Only the 16 MSBs are used to return GPI status. Bit 0 of this slot indicates the
GPI status. When a GPI changes state, this bit gets set for one frame by the codec. This bit can
cause an interrupt to the processor if enabled via the Global Control register.
Reads from 54h/D4h are not transmitted across the link in slot 1 and 2. The data from the most
recent slot 12 is returned on reads from offset 54h/D4h.
Register Access
In the ICH2 implementation of the AC-link, up to two codecs can be connected to the SDOUT pin.
The following mechanism is used to address the primary and secondary codecs individually.
The primary device uses bit 19 of slot 1 as the direction bit to specify read or write. Bits [18:12] of
slot 1 are used for the register index. For I/O writes to the primary codec, the valid bits [14:13] for
slots 1 and 2 must be set in slot 0, as shown in
Table 5-92
. Slot 1 is used to transmit the register
address and slot 2 is used to transmit data. For I/O reads to the primary codec, only slot 1 should be
valid since only an address is transmitted. For I/O reads, only slot 1 valid bit is set; for I/O writes,
both slots 1 and 2 valid bits are set.
The secondary codec registers are accessed using slots 1 and 2 as described above, however the slot
valid bits for slots 1 and 2 are marked invalid in slot 0 and the codec ID bit 0 (bit 0 of slot 0) is set
to 1. This allows the secondary codec to monitor the slot valid bits of slots 1and 2, and bit 0 of slot
0 to determine if the access is directed to the secondary codec. If the register access is targeted to
the secondary codec, slot 1 and 2 will contain the address and data for the register access. Since
slots 1 and 2 are marked invalid, the primary codec will ignore these accesses.
Table 5-92. Output Tag Slot 0
Bit
Primary Access
Example
Secondary Access
Example
Description
15
1
1
Frame Valid
14
1
0
Slot 1 Valid, Command Address bit (Primary codec only)
13
1
0
Slot 2 Valid, Command Data bit (Primary codec only)
12:3
X
X
Slot 3-12 Valid
2
0
0
Reserved
1:0
00
01
Codec ID (00 reserved for primary; 01 indicate secondary)
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