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
have the ability to generate the not acknowledge after the transfer of each byte and before
the completion of the transaction. This requirement is important because SMBus does not
provide any other resend signaling. This difference in the use of the NACK signaling has
implications on the specific implementation of the SMBus port, especially in devices that
handle critical system data such as the SMBus host and the SBS components.
NOTE
In the last byte of master receive slave transmit mode, the
master must send a NACK to the bus, so FACK must be
switched off before the last byte transmits.
38.4.5 Resets
The I2C module is disabled after a reset. The I2C module cannot cause a core reset.
38.4.6 Interrupts
The I2C module generates an interrupt when any of the events in the following table
occur, provided that the IICIE bit is set. The interrupt is driven by the IICIF bit (of the
I2C Status Register) and masked with the IICIE bit (of the I2C Control Register 1). The
IICIF bit must be cleared (by software) by writing 1 to it in the interrupt routine. The
SMBus timeouts interrupt is driven by SLTF and masked with the IICIE bit. The SLTF
bit must be cleared by software by writing 1 to it in the interrupt routine. You can
determine the interrupt type by reading the Status Register.
NOTE
In master receive mode, the FACK bit must be set to zero
before the last byte transfer.
Functional description
KL25 Sub-Family Reference Manual, Rev. 3, September 2012
712 Freescale Semiconductor, Inc.
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