The I2C protocol specification states that the IC that initiates a data transfer on the bus is considered the Bus Master. Consequently, at that time, all the other ICs are regarded to be Bus Slaves.
取得控制權的IC會觸發 START condition
(當SCL high時，SDA 從 high -> low)
以引起所有slaves的注意。
當 transferring data 結束後 同樣的IC會觸發 STOP condition
(當SCL high 時，SDA 從 low -> high)
表示 bus 的控制權被釋放。
Transferring data
Once the START condition has been sent, a byte can be transmitted by the MASTER to the SLAVE. This first byte after a start condition will identify the slave on the bus (address) and will select the mode of operation( '1' = Read / '0' = Write ). 收到指定的SLAVE 會回傳 ACK signal by pulling the SDA line low, previously released (SDA high) by the transmitter.
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