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WM8581
w
PP Rev 1.0 March 2006
55
S/PDIF TRANSMITTER
The S/PDIF transmitter generates the S/PDIF frames, and outputs on the SPDIFOP pin. The audio
data for the frame can be taken from one of four sources, selectable using the TXSRC register. The
transmitter can be powered down using the SPDIFTXD register bit. The S/PDIF Transmitter can be
bypassed by setting the REAL_THROUGH register control bit. When set, the SPDIFOP pin sources
the output of the S/PDIF input mux.
REGISTER
ADDRESS
BIT LABEL DEFAULT
DESCRIPTION
1:0
TXSRC[1:0]
00
S/PDIF Transmitter Data Source
00 = S/PDIF received data (see REAL_THROUGH)
01 = ADC digital output data.
10 = Secondary Audio Interface
11 = Audio Interface received data
2
OVWCHAN
0
Overwrite Channel Status
Only used if TXSRC=00. Overwrites the received
channel status data using data read from S/PDIF
transmitter channel status register
0 = Channel data equal to recovered channel data.
1 = Channel data taken from channel status registers.
R30
SPDTXCHAN 0
1Eh
3 REAL_
THROUGH
0
S/PDIF Through Mode Control
0 = SPDIFOP pin sources output of S/PDIF Transmitter
1 = SPDIFOP pins sources output of S/PDIF IN Mux
R51
PWRDN 2
33h
4 SPDIFTXD
1
S/PDIF Transmitter powerdown
0 = S/PDIF Transmitter enabled
1 = S/PDIF Transmitter disabled
Table 47 S/PDIF Transmitter Control
The WM8581 also transmits the preamble and VUCP bits (Validity, User Data, Channel Status and
Parity bits).
Validity Bit
Set to 0 (to indicate valid data) – unless TXSRC=00 (S/PDIF receiver), where Validity is the value
recovered from the S/PDIF input stream by the S/PDIF receiver.
User Data
Set to 0 as User Data configuration is not supported in the WM8581 – if TXSRC=00 (S/PDIF
receiver) User Data is the value recovered from the S/PDIF input stream by the S/PDIF receiver.
Channel Status
The Channel Status bits form a 192-frame block - transmitted at 1 bit per sub-frame. Each sub-frame
forms its own 192-frame block. The WM8581 is a consumer mode device and only the first 40 bits of
the block are used. All data transmitted from the WM8581 is stereo, so the channel status data is
duplicated for both channels. The only exception to this is the channel number bits (23:20) which can
be changed to indicate whether the channel is left or right in the stereo image. Bits within this block
can be configured by setting the Channel Status Bit Control registers (see Table 48 to Table 52). If
TXSRC=00 (S/PDIF receiver), the Channel Status bits are transmitted with the same values
recovered by the receiver – unless OVWCHAN is set, in which case they are set by the S/PDIF
transmitter channel status registers.
Parity Bit
This bit maintains even parity for data as a means of basic error detection. It is generated by the
transmitter.
For further details of all channel status bits, refer to IEC-60958-3.