ST72734 datasheet(89/144 Pages) STMICROELECTRONICS

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ST72774/ST727754/ST72734

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I²C SINGLE MASTER BUS INTERFACE (Cont’d)

4.7.4 Functional Description (Master Mode)

Refer to the CR, SR1 and SR2 registers in Section

4.7.5. for the bit definitions.

By default the I2C interface operates in idle mode

(M/IDL bit is cleared) except when it initiates a

transmit or receive sequence.

To switch from default idle mode to Master mode a

Start condition generation is needed.

Start condition and Transmit Slave address

Setting the START bit causes the interface to

switch to Master mode (M/IDL bit set) and

generates a Start condition.

Once the Start condition is sent:

– The EVF and SB bits are set by hardware with

an interrupt if the ITE bit is set.

Then the master waits for a read of the SR1

the Slave address byte, holding the SCL line low

(see Figure 54 Transfer sequencing EV1).

Then the slave address byte is sent to the SDA line

via the internal shift register.

After completion of this transfer (and acknowledge

from the slave if the ACK bit is set):

– The EVF bit is set by hardware with interrupt

generation if the ITE bit is set.

Then the master waits for a read of the SR1

example set PE bit), holding the SCL line low

(see Figure 54 Transfer sequencing EV2).

the

master

must

enter

Receiver

Transmitter mode.

Master Receiver

Following the address transmission and after SR1

and CR registers have been accessed, the master

receives bytes from the SDA line into the DR

byte the interface generates in sequence:

– Acknowledge pulse if if the ACK bit is set

– EVF and BTF bits are set by hardware with an in-

terrupt if the ITE bit is set.

Then the interface waits for a read of the SR1

holding the SCL line low (see Figure 54 Transfer

sequencing EV3).

To close the communication: before reading the

last byte from the DR register, set the STOP bit to

generate the Stop condition. The interface goes

automatically back to idle mode (M/IDL bit

cleared).

Note: In order to generate the non-acknowledge pulse af-

ter the last received data byte, the ACK bit must be

cleared just before reading the second last data

byte.

Master Transmitter

Following the address transmission and after SR1

from the DR register to the SDA line via the internal

shift register.

The master waits for a read of the SR1 register

followed by a write in the DR register, holding the

SCL line low (see Figure 54 Transfer sequencing

EV4).

When the acknowledge bit is received, the

interface sets:

– EVF and BTF bits with an interrupt if the ITE bit

is set.

To close the communication: after writing the last

byte to the DR register, set the STOP bit to

generate the Stop condition. The interface goes

automatically back to idle mode (M/IDL bit

cleared).

Error Case

– AF: Detection of a non-acknowledge bit. In this

case, the EVF and AF bits are set by hardware

with an interrupt if the ITE bit is set. To resume,

set the START or STOP bit.

Note: The SCL line is not held low.

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