K60P100M100SF2RM Datasheet, PDF (1467/1809 Pages) Freescale Semiconductor, Inc – K60 Sub-Family Reference Manual

Start
T _LOW:SEXT
Chapter 50 Inter-Integrated Circuit (I2C)
Stop
T _LOW:MEXT
ClkAck
T _LOW:MEXT
ClkAck
T _LOW:MEXT
SCL
SDA
Figure 50-40. Timeout measurement intervals
A master is allowed to abort the transaction in progress to any slave that violates the
T_LOW:SEXT or T_TIMEOUT,MIN specifications. To abort the transaction, the master issues a
STOP condition at the conclusion of the byte transfer in progress. When a slave, the I2C
module must not cumulatively extend its clock cycles for a period greater than
T_LOW:SEXT during any message from the initial START to the STOP. When CSMBCLK
TIMEOUT SEXT occurs, SEXT rises and also triggers SLTF.
NOTE
CSMBCLK TIMEOUT SEXT and CSMBCLK TIMEOUT
MEXT are optional functions that are implemented in the
second step.
50.4.4.2 FAST ACK and NACK
To improve reliability and communication robustness, implementation of packet error
checking (PEC) by SMBus devices is optional for SMBus devices but required for
devices participating in and only during the address resolution protocol (ARP) process.
The PEC is a CRC-8 error checking byte, calculated on all the message bytes. The PEC is
appended to the message by the device that supplied the last data byte. If the PEC is
present but not correct, a NACK is issued by the receiver. Otherwise an ACK is issued.
In order to calculate the CRC-8 by software, this module can hold the SCL line low after
receiving the eighth SCL (8th bit) if this byte is a data byte. So software can determine
whether an ACK or NACK should be sent to the bus by setting or clearing the TXAK bit
if the FACK (fast ACK/NACK enable) bit is enabled.
SMBus requires a device always to acknowledge its own address, as a mechanism to
detect the presence of a removable device (such as a battery or docking station) on the
bus. In addition to indicating a slave device busy condition, SMBus uses the NACK
mechanism to indicate the reception of an invalid command or invalid data. Because such
a condition may occur on the last byte of the transfer, SMBus devices are required to
K60 Sub-Family Reference Manual, Rev. 6, Nov 2011
Freescale Semiconductor, Inc.
1467