TDA7541 datasheet(40/76 Pages) STMICROELECTRONICS

40 / 76 page

Functional description

TDA7541

40/76

Data transition

Data transition on the SDA line must only occur when the clock SCL is LOW. SDA transitions

while SCL is HIGH will be interpreted as START or STOP condition.

Start condition

A start condition is defined by a HIGH to LOW transition of the SDA line while SCL is at a

stable HIGH level. This "START" condition must precede any command and initiate a data

transfer onto the bus. The device continuously monitors the SDA and SCL lines for a valid

START and will not response to any command if this condition has not been met.

Stop condition

A STOP condition is defined by a LOW to HIGH transition of the SDA while the SCL line is at

a stable HIGH level. This condition terminates the communication between the devices and

forces the bus-interface of the device into the initial condition.

Acknowledge

Indicates a successful data transfer. The transmitter will release the bus after sending 8 bits

of data. During the 9th clock cycle the receiver will pull the SDA line to LOW level to indicate

it receives the eight bits of data.

Data transfer

During data transfer the device samples the SDA line on the leading edge of the SCL clock.

Therefore, for proper device operation the SDA line must be stable during the SCL LOW to

HIGH transition.

Device addressing

To start the communication between two devices, the bus master must initiate a start

instruction sequence, followed by an eight bit word corresponding to the address of the

device it is addressing.

The most significant 6 bits of the slave address are the device type identifier.

The TDA7541 device type is fixed as "110001".

The next significant bit is used to address a particular device of the previous defined type

connected to the bus.

The state of the hardwired PIN 57 defines the state of this address bit. Using this feature up

to two devices could be connected on the same bus. When PIN 57 is connected to VCC via

an external resistor of about 82k

Ω the address bit "1" is selected. Please note: in this case

the AM part doesn't work. Otherwise the address bit "0" is selected (FM and AM is working).

Therefore a double FM tuner concept is possible.

The last bit of the start instruction defines the type of operation to be performed:

–

When set to "1", a read operation is selected

–

When set to "0", a write operation is selected

The TDA7541 connected to the bus will compare their own hardwired address with the slave

address being transmitted, after detecting a START condition. After this comparison, the

TDA7541 will generate an "acknowledge" on the SDA line and will do either a read or a write

operation according to the state of R/W bit.

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