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555
I2C Master/Slave Interface
Software driver
The I
2
C master software driver uses three commands only:
M_READ to start a read sequence
M_WRITE to start a write sequence
M_STOP to give up the I
2
C bus
If, during a read or write sequence, another M_READ or M_WRITE is requested by the
ARM CPU, a restart is performed on the I
2
C bus. This opens the opportunity to provide
a new slave device address in the MAster Address register before the command
request.
The I
2
C slave high level driver identifies one command: S_STOP, to discontinue a
transaction. After this command, the slave remains inactive until the next start
condition on the I
2
C bus. If a slave is accessed by a master, it generates S_RX_DATA
and
S_TX_DATA interrupts (see "Master/slave interrupt codes" on page 553). To
distinguish the transactions from each other, special
S_RX_DATA_1ST and S_TX_DATA_1ST
interrupts are generated for the transmitted byte.