Aes3 transmitter, 2 txn and txp drivers, Cs8427 – Cirrus Logic CS8427 User Manual
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CS8427
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DS477F5
7. AES3 TRANSMITTER
The AES3 transmitter encodes and transmits au-
dio and digital data according to the AES3,
IEC60958 (S/PDIF), and EIAJ CP-1201 interface
standards. Audio and control data are multiplexed
together and bi-phase, mark encoded. The result-
ing bit stream is driven to an output connector ei-
ther directly or through a transformer.
The transmitter clock may be derived from the
clock input pin OMCK, or from the incoming data.
If OMCK is asynchronous to the data source, an in-
terrupt bit (TSLIP) is provided that will go high ev-
ery time a data sample is dropped or repeated. Be
aware that the pattern of slips does not have hys-
teresis and so the occurrence of the interrupt con-
dition is not deterministic.
The channel status (C) and user channel (U) bits in
the transmitted data stream are taken from storage
areas within the CS8427. The user can manually
access the internal storage or configure the
CS8427 to run in one of several automatic modes.
The Appendix: Channel Status and User Data
Buffer Management provides detailed descriptions
of each automatic mode and describes methods of
manually accessing the storage areas. The trans-
mitted user data can optionally be input through
the U pin, under the control of a control port regis-
ter bit.
shows the timing requirements for
clocking U data through the U pin.
7.1
Transmitted Frame and Channel
Status Boundary Timing
The TCBL pin is used to control or indicate the start
of transmitted channel status block boundaries and
may be used as an input or output.
In some applications, it may be necessary to con-
trol the precise timing of the transmitted AES3
frame boundaries. This may be achieved in three
ways:
1) With TCBL set to input, driving TCBL high for
>3 OMCK clocks will cause a frame start, as well as
a new channel status block start.
2) If the AES3 output comes from the AES3 input, set-
ting TCBL as output will cause AES3 output frame
boundaries to align with AES3 input frame bound-
aries.
3) If the AES3 output comes from the serial audio in-
put port while the port is in slave mode and TCBL
is set to output, the start of the A channel sub-frame
will be aligned with the leading edge of IL-CK.
7.2
TXN and TXP Drivers
The line drivers are low skew, low impedance, dif-
ferential outputs capable of driving cables directly.
Both drivers are set to ground during reset
(RST = low), when no AES3 transmit clock is pro-
vided, and optionally under the control of a register
bit. The CS8427 also allows immediate mute of the
AES3 transmitter audio data through a control reg-
ister bit.
External components are used to terminate and
isolate the external cable from the CS8427. These
components are detailed in