Howdy Sungjin,
I would make certain that pin12 (SPI/I2C) pin is "low" enabling I2C mode. If A0/A1/A2 are ground, then the slave address will be the 7bit binary 1100001.
I've copied an image for an I2C write below. More information can be obtained from pg.51 of AMC7812 ds.
The following is an I2C Write sequence.
1. The master device asserts a start condition.
2. The master then sends the 7-bit AMC7812 slave address followed by a zero for the direction bit, indicating a
write operation. Note that the correct slave address is 0xC2 (11000010)
Slave address (0xC2 - write) (0xC3-read)
3. The AMC7812 asserts an acknowledge signal on SDA.
4. The master sends a register address.
5. The AMC7812 asserts an acknowledge signal on SDA.
6. The master sends a data byte of the high byte of the register (D15:D8).
7. The AMC7812 asserts an acknowledge signal on SDA.
8. The master sends a data byte of the low byte of the register (D7:D0).
9. The AMC7812 asserts an acknowledge signal on SDA.
10. The master asserts a stop condition to end the transaction.
