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AS8650

Datasheet - Application In form atio n

8.2 Inter-Integrated Circuit (I2C) Interface

I2C is a bidirectional 2 line bus interface with a serial data line (SDA) and a serial clock line (SCLK) for inter IC control. This interface is only slave

interface and only microcontroller can start and stop the I2C operation. The overview of I2C protocol is shown in Figure 22. A HIGH to LOW

transition on SDA line while SCLK is HIGH is the START (S) condition and a LOW to HIGH transition on SDA line while SCLK is HIGH is the

STOP (P) condition, as shown in Figure 22. The START and STOP conditions should always be generated by the microcontroller. After the

START condition, microcontroller has to make sure that data on SDA line must be stable during the HIGH period of SCLK. The data should only

change when SCLK line is LOW. The Bus is busy after the START condition and it is free after the STOP condition. Any number of data bytes

can be transmitted between START and STOP. Each byte is followed by an acknowledgement (which is the ninth bit). The data transmitter

always receives an acknowledgement from the data receiver at end of each byte. The data transmitter releases the SDA bus at start of LOW

period of 8th clock pulse and data receiver acknowledges by pulling the SDA to LOW during the LOW period of the SCLK. The Data receiver

releases the bus at start of LOW period of 9th clock pulse of the SCLK and data transmitter gets the data bus.The AS8650 does not support

general call address, START byte and high-speed mode.

Figure 22. I2C Bus Protocol

8.2.1 I2C Write Operation

After the START condition, microcontroller has to send, in the first byte, the 7-bit slave address and 0 into the R/W bit as shown in Figure 23. The

microcontroller has to send the address of the register to be written in the second byte. The first 3 MSB bits are reserved and remaining 5 bits are

used as address bits. The data is sent starting from MSB to LSB. The AS8650 sends acknowledgement on 9th clock pulse. In the next byte (3rd

byte) microcontroller has to send the data to be written into addressed register. If it is a single write operation, after receiving the

acknowledgment from AS8650, microcontroller has to send START or STOP condition, as shown in Figure 23. In case of auto increment write

operation, microcontroller should not generate START or STOP condition after the third byte. If microcontroller continuously writes then address

pointer rolls back to the starting register address after reaching the last register address. Data bytes coming from the microcontroller are written

at the consecutive address locations, starting from the address sent in first data byte. After each data byte, direction of the bus line changes and

AS8650 acknowledges by pulling the SDA line LOW. To terminate the write operation microcontroller has to generate STOP or repeated START

condition. For details, see Figure 24.

Figure 23. I2C Write Operation

SDA

S

12

8

9

SCLK

MSB

ACK

34

56

7

12

8

9

34

56

7

R/W

7 bit Slave address

LSB

8 bit Data

12

8

9

34

56

7

S

or

P

8 bit Data

ACK

ACK

12

8

9

SCLK

MSB

SDA

34

56

7

12

8

9

34

56

7

LSB

12

8

9

34

56

7

A

AA

acknowledge

from slave

acknowledge

from slave

acknowledge

from slave

register address

data to register

S

or

P

R/W

Slave address

S

A0

A1

A2

A3

A4