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eUSCI_B Operation – I
2
C Mode
20.3.5.2.2 I
2
C Master Receiver Mode
After initialization, master receiver mode is initiated by writing the desired slave address to the
UCBxI2CSA register, selecting the size of the slave address with the UCSLA10 bit, clearing UCTR for
receiver mode, and setting UCTXSTT to generate a START condition.
The eUSCI_B module checks if the bus is available, generates the START condition, and transmits the
slave address. The UCTXSTT flag is cleared as soon as the complete address is sent.
After the acknowledge of the address from the slave, the first data byte from the slave is received and
acknowledged and the UCRXIFG flag is set. Data is received from the slave, as long as:
•
No automatic STOP is generated
•
The UCTXSTP bit is not set
•
The UCTXSTT bit is not set
If a STOP condition was generated by the eUSCI_B module, the UCSTPIFG is set. If UCBxRXBUF is not
read, the master holds the bus during reception of the last data bit and until the UCBxRXBUF is read.
If the slave does not acknowledge the transmitted address, the not-acknowledge interrupt flag
UCNACKIFG is set. The master must react with either a STOP condition or a repeated START condition.
A STOP condition is either generated by the automatic STOP generation or by setting the UCTXSTP bit.
The next byte received from the slave is followed by a NACK and a STOP condition. This NACK occurs
immediately if the eUSCI_B module is currently waiting for UCBxRXBUF to be read.
If a RESTART is sent, UCTR may be set or cleared to configure transmitter or receiver, and a different
slave address may be written into UCBxI2CSA if desired.
shows the I
2
C master receiver operation.
NOTE:
Consecutive master transactions without repeated START
When performing multiple consecutive I
2
C master transactions without the repeated START
feature, the current transaction must be completed before the next one is initiated. This can
be done by ensuring that the transmit STOP condition flag UCTXSTP is cleared before the
next I
2
C transaction is initiated with setting UCTXSTT = 1. Otherwise, the current transaction
might be affected.
544
SLAU272C – May 2011 – Revised November 2013
Enhanced Universal Serial Communication Interface (eUSCI) – I
2
C Mode
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