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I2C Protocol Sequence

I2C require two bus line – SDA and SCL
Most I2C devices can communicate at 100 kHz or 400 kHz.

Start/Stop Condition:
Start and Stop condition are always generated by the master.
Each I2C command initiated by master device starts with a START condition and ends with a STOP condition. For both conditions SCL has to be high. A high to low transition of SDA is considered as START and a low to high transition as STOP.

Generally our i2c driver perform the following sequence:
    Start condition – write operation (sub-address)-start condition- Read operation (data)-stop condition.
    Need to send STOP bit when the whole process reading is done. To terminate a read/write sequence a stop signal must be sent.

Please make sure with below Read/Write sequences,
a.Write Sequence
 1) Send the start condition
 2) Send the slave address
 3) Check for the acknowledge
 4) Send the sub-address to be written to
 5) Check for the acknowledge from
 6) Send the data to write to specified sub address
 7) Check for the acknowledge
 8) If No-acknowledge send the stop condition
 9) Send a stop condition

b. Read Sequence
1) Send the start condition
2) Send the slave address
3) check for the acknowledge
4) Send the sub-address to be read from
5) check for the acknowledge
6) Send the start condition
7) Send the slave address
8) check for the acknowledge
9) If No-acknowledge send the stop condition
10) If acknowledged read the data from specified sub-address
12) Send a No-Acknowledge
13) Send a stop condition

Here we can find the more details about i2c bus specification and also timing related details I2C Bus Specification and User Manual

Note: Some i2c drivers work with 7 bit addressing, if your software/tool is using 7-bit i2c address, In that case, we need to right shift the 8 bit map address to one.
For example: 0x98 IO Map   –   8 bit address
                 0x98>>1 =0x4C – 7 bit address
Please crosscheck: 0x98 is an 8-bit I2C address. In other words, it assumes the software/tool is using 8-bit I2C addresses.
In-case if your software/tool is using 7-bit I2C addresses (fairly common), you should use 0x4C instead.

NACK(No ACK):  I2C reset is the only write that will no ACK back. The reset bit resets the I2c engine before it has a chance to ACK back.The I2C master controller will receive a no acknowledge condition on the ninth clock cycle when chip Reset is implemented.