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Functional description
45.5.4 System management bus specification
SMBus provides a control bus for system and power management related tasks. A system
can use SMBus to pass messages to and from devices instead of tripping individual
control lines.
Removing the individual control lines reduces pin count. Accepting messages ensures
future expandability. With the system management bus, a device can provide
manufacturer information, tell the system what its model/part number is, save its state for
a suspend event, report different types of errors, accept control parameters, and return its
status.
45.5.4.1 Timeouts
The T
parameter allows a master or slave to conclude that a defective device
TIMEOUT,MIN
is holding the clock low indefinitely or a master is intentionally trying to drive devices
off the bus. The slave device must release the bus (stop driving the bus and let SCL and
SDA float high) when it detects any single clock held low longer than T
Devices that have detected this condition must reset their communication and be able to
receive a new START condition within the timeframe of T
SMBus defines a clock low timeout, T
cumulative clock low extend time for a slave device, and specifies T
cumulative clock low extend time for a master device.
45.5.4.1.1 SCL low timeout
If the SCL line is held low by a slave device on the bus, no further communication is
possible. Furthermore, the master cannot force the SCL line high to correct the error
condition. To solve this problem, the SMBus protocol specifies that devices participating
in a transfer must detect any clock cycle held low longer than a timeout value condition.
Devices that have detected the timeout condition must reset the communication. When
the I2C module is an active master, if it detects that SMBCLK low has exceeded the
value of T
TIMEOUT,MIN
byte in the transfer process. When the I2C module is a slave, if it detects the
T
condition, it resets its communication and is then able to receive a new
TIMEOUT,MIN
START condition.
1254
TIMEOUT
, it must generate a stop condition within or after the current data
KV4x Reference Manual, Rev. 2, 02/2015
Preliminary
TIMEOUT,MAX
, of 35 ms, specifies T
.
TIMEOUT,MIN
.
as the
LOW:SEXT
as the
LOW:MEXT
Freescale Semiconductor, Inc.
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