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WM8777
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.
REGISTER
ADDRESS
BIT
LABEL
DEFAULT
DESCRIPTION
(41h)
2:1
TXSRC[1:0]
00
S/PDIF Transmitter Data Source.
00 = S/PDIF received data.
Interface Source
Select
01 = ADC digital output data.
10 = Secondary Audio Interface received data
11 = Primary Audio Interface Received data.
3
6
TXRXTHRU
SPDIFTXD
0
1
Only used if TXSRC==00. Configures only the Channel
Bit in the S/PDIF frame.
0 = Channel data equal to recovered channel data.
1 = Channel data taken from channel status registers.
SPDIF_TX powerdown
(1Ah)
Powerdown
Control
0 = SPDIF_TX enabled
1 = SPDIF_TX disabled
Table 33 S/PDIF Tx Control
The WM8777 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 set by the
receiver.
USER DATA
Set to 0 as User Data configuration is not supported in the WM8777 – if TXSRC=00 (S/PDIF
receiver) User Data is set by the 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 WM8777 is a consumer mode device and only the first 40 bits of
the block are used. All data transmitted from the WM8777 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 if the channel is left or right in the stereo image. Bits within this block can be
configured by setting the Channel Bit Control registers (see Tables 28-32 ). If TXSRC is the S/PDIF
receiver, the Channel bits are transmitted with the same values recovered by the receiver – unless
TXRXTHRU is set, in which case they are set by the registers.
Note that the WM8777 expects to receive channel status data in consumer format. The channel
status bits are defined differently for professional mode. The definitions on the following page do not
hold for professional mode.
PARITY BIT
This bit maintains even parity for data as a means of basic error detection. It is generated by the
transmitter.
PP Rev 1.94 November 2004
47
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WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
