RM0312 datasheet(172/275 Pages) STMICROELECTRONICS

172 / 275 page

Inter-integrated circuit (I2C) interface

RM0312

172/275

DocID022352 Rev 3

19.3

I2C general description

In addition to receiving and transmitting data, this interface converts it from serial to parallel

format and vice versa. The interrupts are enabled or disabled by software. The interface is

connected to the I2C bus by a data pin (SDA) and by a clock pin (SCL). It can be connected

with a standard (up to 100 kHz), or fast (up to 400 kHz) I2C bus.

Mode selection

The interface can operate in one of the four following modes:

•

Slave transmitter

•

Slave receiver

•

Master transmitter

•

Master receiver

By default, it operates in slave mode. The interface automatically switches from slave to

master, after it generates a START condition and from master to slave, if an arbitration loss

or a STOP generation occurs, allowing Multi-Master capability.

Communication flow

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. Both

start and stop conditions are generated in master mode by software.

In Slave mode, the interface is capable of recognizing its own addresses (7- or 10-bit), and

the General Call address. The General Call address detection may be enabled or disabled

by software.

Data and addresses are transferred as 8-bit bytes, MSB first. The first byte(s) following the

start condition contain the address (one in 7-bit mode, two in 10-bit mode). The address is

always transmitted in Master mode.

A 9th clock pulse follows the 8 clock cycles of a byte transfer, during which the receiver must

send an acknowledge bit to the transmitter. Refer to the following figure.

Figure 65. I2C bus protocol

Acknowledge may be enabled or disabled by software. The I2C interface addresses (dual

addressing, 7-/10-bit and/or general call address) can be selected by software.

SCL

SDA

MSB

ACK

STOP

START

CONDITION

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