PixArt Imaging Inc.
PAS109B
CMOS Image Sensor IC
5. I
2
C Bus
PAS109B supports I2C-bus transfer protocol and is acting as slave device. The 7 bits unique slave address is
1000000 and supports receiving / transmitting speed up to 400kHz.
5.1 I
2
C bus overview
Only two wires SDA (serial data) and SCL (serial clock) carry information between the devices connected
to the I2C bus. Normally both SDA and SCL lines are open collector structure and pull high by external
pull-up resistors.
Only the master can initiates a transfer (start), generates clock signals, and terminates a transfer (stop).
Start and stop condition: A high to low transition of the SDA line while SCL is high defines a start
condition. A low to high transition of the SDA line while SCL is high defines a stop condition. Please
refer to Fig 5.1.
Valid data: The data on the SDA line must be stable during the high period of the SCL clock. Within each
byte, MSB is always transferred first. Read/write control bit is the LSB of the first byte. Please refer to
Fig 5.2.
Both the master and slave can transmit and receive data from the bus.
Acknowledge: The receiving device should pull down the SDA line during high period of the SCL clock
line when a complete byte was transferred by transmitter. In the case of a master received data from a
slave, the master does not generate an acknowledgment on the last byte to indicate the end of a master
read cycle.
SDA
SCL
S
Start
Condition
P
Stop
Condition
Fig 5.1
Start and Stop Conditions
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6
V1.1, Mar. 2002
PixArt Imaging Inc.
E-mail:
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PIXART [ PIXART IMAGING INC. ]
