sta003t STMicroelectronics, sta003t Datasheet - Page 9

• Manufacturer Part Number: sta003t
• Description: Mpeg 2.5 Layer Iii Audio Decoder
• Manufacturer: STMicroelectronics

3 - I
The STA003T supports the I
tocol defines any device that sends data on to the
bus as a transmitter and any device that reads
the data as a receiver. The device that controls
the data transfer is known as the master and the
others as the slave. The master always starts the
transfer and provides the serial clock for synchro-
nisation. The STA003T is always a slave device
in all its communications.
3. 1 - COMMUNICATION PROTOCOL
3.1.0 - Data transition or change
Data changes on the SDA line must only occur
when the SCL clock is low. SDA transition while
the clock is high are used to identify START or
STOP condition.
3.1.1 - Start condition
START is identified by a high to low transition of
the data bus SDA signal while the clock signal
SCL is stable in the high state. A START condi-
tion must precede any command for data transfer.
3.1.2 - Stop condition
STOP is identified by low to high transition of the
data bus SDA signal while the clock signal SCL is
stable in the high state. A STOP condition termi-
nates communications between STA003T and
the bus master.
3.1.3 - Acknowledge bit
An acknowledge bit is used to indicate a success-
ful data transfer. The bus transmitter, either mas-
ter or slave, releases the SDA bus after sending
8 bit of data.
During the 9th clock pulse the receiver pulls the
SDA bus low to acknowledge the receipt of 8 bits
of data.
3.1.4 - Data input
During the data input the STA003T samples the
Figure 9. Write Mode Sequence
MULTIBYTE
WRITE
WRITE
BYTE
2
C BUS SPECIFICATION
START
START
DEV-ADDR
DEV-ADDR
2
C protocol. This pro-
RW
RW
ACK
ACK
SUB-ADDR
SUB-ADDR
ACK
ACK
SDA signal on the rising edge of the clock SCL.
For correct device operation the SDA signal has
to be stable during the rising edge of the clock
and the data can change only when the SCL line
is low.
3.2 - DEVICE ADDRESSING
To start communication between the master and
the STA003T, the master must initiate with a start
condition. Following this, the master sends onto
the SDA line 8 bits (MSB first) corresponding to
the device select address and read or write
mode.
The 7 most significant bits are the device address
identifier, corresponding to the I
For the STA003T these are fixed as 1000011.
The 8th bit (LSB) is the read or write operation
RW, this bit is set to 1 in read mode and 0 for
write mode. After a START condition the
STA003T identifies on the bus the device ad-
dress and, if a match is found, it acknowledges
the identification on SDA bus during the 9th bit
time. The following byte after the device identifi-
cation byte is the internal space address.
3.3 - WRITE OPERATION (see fig. 9)
Following a START condition the master sends a
device select code with the RW bit set to 0.
The STA003T acknowledges this and waits for
the byte of internal address.
After receiving the internal bytes address the
STA003T again responds with an acknowledge.
3.3.1 - Byte write
In the byte write mode the master sends one data
byte, this is acknowledged by STA003T. The
master then terminates the transfer by generating
a STOP condition.
3.3.2 - Multibyte write
The multibyte write mode can start from any inter-
nal address. The transfer is terminated by the
master generating a STOP condition.
DATA IN
DATA IN
ACK
ACK
STOP
D98AU825B
DATA IN
2
C bus definition.
ACK
STA003T
STOP
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