RM0312 datasheet(176/275 Pages) STMICROELECTRONICS

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Inter-integrated circuit (I2C) interface

RM0312

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DocID022352 Rev 3

Figure 68. Transfer sequence diagram for slave receiver

1. Legend:

S= Start, Sr = Repeated Start, P= Stop, A= Acknowledge, NA= Non-acknowledge, EVx= Event (with

interrupt if ITEVTEN=1)

EV1: ADDR =1, cleared by reading SR1 register followed by reading SR3.

EV2: RXNE=1, cleared by reading DR register.

EV4: STOPF=1, cleared by reading SR1 register followed by writing CR2 register

2. EV1 event stretches SCL low until the end of the corresponding software sequence.

3. EV2 event stretches SCL low if the software sequence is not completed before the end of the next byte

reception.

4. After checking the SR1 register content, the user should perform the complete clearing sequence for each

flag found set. Thus, for the ADDR and STOPF flags, the following sequence is recommended inside the

I2C interrupt routine:

READ SR1

if (ADDR == 1) {READ SR1; READ SR3}

if (STOPF == 1) {READ SR1; WRITE CR2}

The purpose is to make sure that both ADDR and STOPF flags are cleared if both are found set.

5. See also: Note 8 on page 192.

Closing slave communication

After the last data byte is transferred, a Stop condition is generated by the master. The

interface detects this condition and sets the STOPF bit and generates an interrupt if the

ITEVTEN bit is set.

STOPF is cleared by a read of the SR1 register followed by a write to the CR2 register (refer

to EV4 in Figure 68: Transfer sequence diagram for slave receiver).

19.4.2

I2C master mode

In Master mode, the I2C interface initiates a data transfer and generates the clock signal. A

serial data transfer always begins with a Start condition and ends with a Stop condition.

Master mode is selected as soon as the Start condition is generated on the bus with a

START bit.

The following is the required sequence in master mode.

•

Program the peripheral input clock in I2C_FREQR Register in order to generate correct

timings.

•

Configure the clock control registers

•

Configure the rise time register

•

Program the I2C_CR1 register to enable the peripheral

•

Set the START bit in the I2C_CR2 register to generate a Start condition

7-bit slave receiver

10-bit slav e receiver

S Address

Data1

Data2

.....

DataN

EV1

EV2

EV4

S Header

Address

Data1

.....

DataN

EV1

EV2

EV4

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