15.3.7 Master Operation
A bus transaction is initiated by transmitting a START condition (S) on the bus. This is done by setting the START bit in I2Cn_CMD. The
command schedules a START condition, and makes the I
2
C module generate a start condition whenever the bus becomes free.
The I
2
C-bus is considered busy whenever another device on the bus transmits a START condition. Until a STOP condition is detected,
the bus is owned by the master issuing the START condition. The bus is considered free when a STOP condition is transmitted on the
bus. After a STOP is detected, all masters that have data to transmit send a START condition and begin transmitting data. Arbitration
ensures that collisions are avoided.
When the START condition has been transmitted, the master must transmit a slave address (ADDR) with an R/W bit on the bus. If this
address is available in the transmit buffer, the master transmits it immediately, but if the buffer is empty, the master holds the I
2
C-bus
while waiting for software to write the address to the transmit buffer.
After the address has been transmitted, a sequence of bytes can be read from or written to the slave, depending on the value of the
R/W bit (bit 0 in the address byte). If the bit was cleared, the master has entered a master transmitter role, where it now transmits data
to the slave. If the bit was set, it has entered a master receiver role, where it now should receive data from the slave. In either case, an
unlimited number of bytes can be transferred in one direction during the transmission.
At the end of the transmission, the master either transmits a repeated START condition (Sr) if it wishes to continue with another trans-
fer, or transmits a STOP condition (P) if it wishes to release the bus. When operating in the master mode, HFPERCLK frequency must
be higher than 2 MHz for Standard-mode, 9 MHz for Fast-mode, and 20 MHz for Fast-mode Plus.
EFM32JG1 Reference Manual
I2C - Inter-Integrated Circuit Interface
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