TDA1315 Philips Semiconductors, TDA1315 Datasheet - Page 11

• Manufacturer Part Number: TDA1315
• Description: Digital audio input/output circuit DAIO
• Manufacturer: Philips Semiconductors

Philips Semiconductors
Table 3 First byte of transferred channel status
Table 4 Second byte of transferred channel status
User data
In principle, the user data bits may be used in any way
required by the user. In order to guarantee compatibility
between signals of any source, attempts have been made
for the standardization of a user data format. The basic
idea is to transfer ‘messages’ that consist of ‘information
units’. As messages are, typically, asynchronous with the
IEC audio block structure, their transfer relies on software
protocol. Currently, the applications for CD subcode and
DAT have been accepted. Their general format complies
with that protocol and can be described as follows:
1995 Jul 17
0 and 1 clock accuracy
2 and 3 sample frequency
User data is transferred in the form of messages.
Messages consist of information units, i.e. groups of
8 bits (bytes).
Messages are separated by more than 8 zero bits (0).
Information units within a message may be separated by
0 up to and including 8 zero bits.
The MSB of each byte is sent first in the user data
channel.
The MSB of each byte is a 1-bit (1, start bit).
For CD subcode, one byte consists of bits 1QRSTUVW.
Digital audio input/output circuit (DAIO)
BIT
BIT
4
5
6
7
0
1
2
3
4
5
6
7
pre-emphasis
copyright
audio/data
consumer/professional use
category code
category code
category code
category code
category code
category code
category code
category code
DESCRIPTION
DESCRIPTION
CHANNEL
CHANNEL
29 and 28
25 and 24
STATUS
STATUS
BIT IN
BIT IN
15
14
13
12
11
10
3
2
1
0
9
8
11
Normally, the exchange of user data between the
TDA1315H and the microcontroller is based on the
general format described above. In the event of CD
subcode, this means that 96 bytes need to be transferred
for each subcode frame. In order to reduce the amount of
data traffic, it is possible to separate the Q-channel bits
from the user data and transfer only them. This mode can
be enabled by a bit in the control register and leads to the
transfers of only 12 bytes per subcode frame. As there is
no check in the TDA1315H whether user data is from a CD
source, this Q-channel decoding can be employed
whenever the user data format permits.
Receive mode
User data bits are extracted from the received IEC
subframes and searched for the beginning of a message.
When Q-channel decoding is disabled (in the control
register), the data bytes of a message are stored in a
buffer for subsequent external interpretation or
processing. Any 0 bits between information units and
between messages are skipped.
It is essential to maintain synchronization of messages,
even if not all bytes of a message can be exchanged with
the microcontroller in a single transfer, or if there are
several messages in the buffer. When user data is
transferred in the general format described earlier, the
beginning of a message is indicated in the buffer by a 1 bit
in the MSB position of the first byte of that message. In all
subsequent bytes of the same message, the MSB will be
zero. This is illustrated in Table 5 for the CD subcode.
The user data buffer is implemented as a FIFO (First-In,
First-Out) with a size of 128 bytes. This allows the storing
of a full CD subcode frame. A synchronization signal at pin
UDAVAIL supports the transfer of user data to the
microcontroller. This signal goes LOW when there is at
least 1 byte of user data in the buffer, and returns HIGH
only after the last received byte has been read. This is
illustrated in Fig.3.
Based on the timing of the CD subcode, the
microcontroller should start reading data within 17 ms after
UDAVAIL has gone LOW, otherwise the buffer will fill
completely and the most recent data will be lost.
Product specification
TDA1315H