ST72321XX Datasheet, PDF (156/243 Pages) STMicroelectronics – PLL for 2x frequency multiplication

I2C bus interface (I2C)
ST72321xx-Auto
16.3
16.3.1
16.3.2
General description
In addition to receiving and transmitting data, this interface converts it from serial to parallel
format and vice versa, using either an interrupt or polled handshake. The interrupts are
enabled or disabled by software. The interface is connected to the I²C bus by a data pin
(SDAI) and by a clock pin (SCLI). It can be connected both with a standard I²C bus and a
fast I²C bus. This selection is made by software.
Mode selection
The interface can operate in the four following modes:
● Slave transmitter/receiver
● Master transmitter/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 in case of arbitration loss or a STOP generation, allowing
then Multimaster capability.
Communication flow
In Master mode, it 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 address (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 Figure 66.
Figure 66. I²C bus protocol
SDA
MSB
ACK
SCL
1
2
8
9
START
CONDITION
STOP
CONDITION
VR02119B
Acknowledge may be enabled and disabled by software.
The I²C interface address and/or general call address can be selected by software.
The speed of the I²C interface may be selected between standard (up to 100 kHz) and fast
I²C (up to 400 kHz).
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Doc ID 13829 Rev 1