2 ac-link serial data input frame, Cs4205 – Cirrus Logic CS4205 User Manual
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CS4205
22
DS489PP4
4.2
AC-Link Serial Data Input Frame
In the serial data input frame, data is passed on the SDATA_IN pin from the CS4205 to the AC ’97 con-
troller. The data format for the input frame is very similar to the output frame. Figure 14 on page 19 illus-
trates the serial port timing.
The PCM capture data from the CS4205 is shifted out MSB first in the most significant 18 bits of each slot.
The least significant 2 bits in each slot will be ‘cleared’. If the host requests PCM data from the AC ’97
Controller that is less than 18 bits wide, the controller should dither and round or just round (but not trun-
cate) to the desired bit depth.
Bits that are reserved or not implemented in the CS4205 will always be returned ‘cleared’.
4.2.1
Serial Data Input Slot Tag Bits (Slot 0)
Codec Ready
Codec Ready. The Codec Ready bit indicates the readiness of the CS4205 AC-link. Immedi-
ately after a Cold Reset this bit will be ‘clear’. Once the CS4205 clocks and voltages are sta-
ble, this bit will be ‘set’. Until the Codec Ready bit is ‘set’, no AC-link transactions should be
attempted by the controller. The Codec Ready bit does not indicate readiness of the DACs,
ADCs, Vref, or any other analog function. Those must be checked in the Powerdown Con-
trol/Status Register (Index 26h) by the controller before any access is made to the mixer reg-
isters. Any accesses to the CS4205 while Codec Ready is ‘clear’ are ignored.
Slot 1 Valid
The Slot 1 Valid bit indicates Slot 1 contains a valid read back address.
Slot 2 Valid
The Slot 2 Valid bit indicates Slot 2 contains valid register read data.
Slot [3:8,11] Valid
The Slot [3:8,11] Valid bits indicate Slot [3:8,11] contains valid capture data from the CS4205
ADCs. If a bit is ‘set’, the corresponding input slot contains valid data. If a bit is ‘cleared’, the
corresponding slot will be ignored.
Slot 12 Valid
The Slot 12 Valid bit indicates Slot 12 contains valid GPIO status data.
4.2.2
Status Address Port (Slot 1)
RI[6:0]
Register Index. The RI[6:0] bits echo the AC ’97 register address when a register read has
been requested in the previous frame. The CS4205 will only echo the register index for a read
access. Write accesses will not return valid data in Slot 1.
SR[3:9,11]
Slot Request. If SRx is ‘set’, this indicates the CS4205 SRC does not need a new sample on
the next AC-link frame for that particular slot. If SRx is ‘clear’, the SRC indicates a new sample
is needed on the following frame. If the VRA bit in the Extended Audio Status/Control Register
(Index 2Ah)
is ‘clear’, the SR[3:9,11] bits are always 0. When VRA is ‘set’, the SRC is enabled
and the SR[3:9,11] bits are used to request data.
Bit 15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
Codec
Ready
Slot 1
Valid
Slot 2
Valid
Slot 3
Valid
Slot 4
Valid
Slot 5
Valid
Slot 6
Valid
Slot 7
Valid
Slot 8
Valid
0
0
Slot 11
Valid
Slot 12
Valid
Reserved
Bit 19
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
Res
RI6
RI5
RI4
RI3
RI2
RI1
RI0
SR3 SR4 SR5 SR6 SR7 SR8 SR9
0
SR11
0
Reserved