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AS8650B

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 AS8650B does not support general call

address, START byte and high-speed mode.

Figure 22. I²C Bus Protocol

8.2.1 I²C Slave Address

The 7-bit slave address of the device is by default set to 0000000.

On request the slave address can be changed in the range from 0000000 to 1111110 through factory settings.

8.2.2 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 AS8650B 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 AS8650B, 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

AS8650B 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