ST STM32F100 Series Reference Manual page 581

RM0041
Bus protocols
The SMBus specification supports up to nine bus protocols. For more details of these
protocols and SMBus address types, refer to SMBus specification version. 2.0. These
protocols should be implemented by the user software.
Address resolution protocol (ARP)
SMBus slave address conflicts can be resolved by dynamically assigning a new unique
address to each slave device. The Address Resolution Protocol (ARP) has the following
attributes:
•
Address assignment uses the standard SMBus physical layer arbitration mechanism
•
Assigned addresses remain constant while device power is applied; address retention
through device power loss is also allowed
•
No additional SMBus packet overhead is incurred after address assignment. (i.e.
subsequent accesses to assigned slave addresses have the same overhead as
accesses to fixed address devices.)
•
Any SMBus master can enumerate the bus
Unique device identifier (UDID)
In order to provide a mechanism to isolate each device for the purpose of address
assignment, each device must implement a unique device identifier (UDID).
For the details on 128-bit UDID and more information on ARP, refer to SMBus specification
version 2.0.
SMBus alert mode
SMBus Alert is an optional signal with an interrupt line for devices that want to trade their
ability to master for a pin. SMBA is a wired-AND signal just as the SCL and SDA signals are.
SMBA is used in conjunction with the SMBus General Call Address. Messages invoked with
the SMBus are two bytes long.
A slave-only device can signal the host through SMBA that it wants to talk by setting ALERT
bit in I2C_CR1 register. The host processes the interrupt and simultaneously accesses all
SMBA devices through the Alert Response Address (known as ARA having a value 0001
100X). Only the device(s) which pulled SMBA low acknowledge the Alert Response
Address. This status is identified using SMBALERT Status flag in I2C_SR1 register. The
host performs a modified Receive Byte operation. The 7 bit device address provided by the
slave transmit device is placed in the 7 most significant bits of the byte. The eighth bit can
be a zero or one.
If more than one device pulls SMBA low, the highest priority (lowest address) device wins
communication rights via standard arbitration during the slave address transfer. After
acknowledging the slave address the device must disengage its SMBA pull-down. If the
host still sees SMBA low when the message transfer is complete, it knows to read the ARA
again.
A host which does not implement the SMBA signal may periodically access the ARA.
For more details on SMBus Alert mode, refer to SMBus specification version 2.0.
Timeout error
There are differences in the timing specifications between I
SMBus defines a clock low timeout, TIMEOUT of 35 ms. Also SMBus specifies TLOW:
Inter-integrated circuit (I2C) interface
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