Sda/Scl Line Control; Smbus - ST STM32F101 Series Reference Manual

Inter-integrated circuit (I2C) interface
15.4.4

SDA/SCL line control

If clock stretching is enabled:
–
–
If clock stretching is disabled in Slave mode:
–
–
–
15.4.5

SMBus

Introduction
The System Management Bus (SMBus) is a two-wire interface through which various
devices can communicate with each other and with the rest of the system. It is based on I
principles of operation. SMBus provides a control bus for system and power management
related tasks. A system may use SMBus to pass messages to and from devices instead of
toggling individual control lines.
The System Management Bus Specification refers to three types of devices. A slave is a
device that is receiving or responding to a command. A master is a device that issues
commands, generates the clocks, and terminates the transfer. A host is a specialized master
that provides the main interface to the system's CPU. A host must be a master-slave and
must support the SMBus host notify protocol. Only one host is allowed in a system.
Similarities between SMBus and I
2 wire bus protocol (1 Clk, 1 Data) + SMBus Alert line optional
Master-slave communication, Master provides clock
Multi master capability
SMBus data format similar to I
328/501
Transmitter mode: If TxE=1 and BTF=1: the interface holds the clock line low
before transmission to wait for the microcontroller to read SR1 and then write the
byte in the Data Register (both buffer and shift register are empty).
Receiver mode: If RxNE=1 and BTF=1: the interface holds the clock line low after
reception to wait for the microcontroller to read SR1 and then read the byte in the
Data Register (both buffer and shift register are full).
Overrun Error in case of RxNE=1 and no read of DR has been done before the
next byte is received. The last received byte is lost.
Underrun Error in case TxE=1 and no write into DR has been done before the next
byte must be transmitted. The same byte will be sent again.
Write Collision not managed.
2
C
2
C 7-bit addressing format
RM0008
(Figure 134).
2
C