Technical Note
BU9880GUL-W
●I2C BUS communication
○I2C BUS data communication
I2C BUS data communication starts by start condition input, and ends by stop condition input. Data is always 8bit long,
and acknowledge is always required after each byte.
I2C BUS carries out data transmission with plural devices connected by 2 communication lines of serial data (SDA) and
serial clock (SCL).
Among devices, there are “master” that generates clock and control communication start and end, and “slave” that is
controlled by addresses peculiar to devices.
EEPROM becomes “slave”. And the device that outputs data to bus during data communication is called “transmitter”,
and the device that receives data is called “receiver”.
SDA
1-7
1-7
1-7
8
9
8
9
8
9
SCL
S
P
START ADDRESS R/W ACK
condition
DATA
ACK
DATA
ACK STOP
condition
Fig.32 Data transfer timing
○Start condition (start bit recognition)
・Before executing each command, start condition (start bit) where SDA goes from 'HIGH' down to 'LOW' when SCL is
'HIGH' is necessary.
・This IC always detects whether SDA and SCL are in start condition (start bit) or not, therefore, unless this condition is
satisfied, any command is executed.
○Stop condition (stop bit recognition)
・Each command can be ended by SDA rising from 'LOW' to 'HIGH' when stop condition (stop bit), namely, SCL is 'HIGH'
○Acknowledge (ACK) signal
・This acknowledge (ACK) signal is a software rule to show whether data transfer has been made normally or not. In
master and slave, the device (µ-COM at slave address input of write command, read command, and this IC at data
output of read command) at the transmitter (sending) side releases the bus after output of 8bit data.
・The device (this IC at slave address input of write command, read command, and µ-COM at data output of read
command) at the receiver (receiving) side sets SDA 'LOW' during 9 clock cycles, and outputs acknowledge signal (ACK
signal) showing that it has received the 8bit data.
・This IC, after recognizing start condition and slave address (8bit), outputs acknowledge signal (ACK signal) 'LOW'.
・Each write action outputs acknowledge signal) (ACK signal) 'LOW', at receiving 8bit data (word address and write data).
・Each read action outputs 8bit data (read data), and detects acknowledge signal (ACK signal) 'LOW'. When
acknowledge signal (ACK signal) is detected, and stop condition is not sent from the master (µ-COM) side, this IC
continues data output. When acknowledge signal (ACK signal) is not detected, this IC stops data transfer, and
recognizes stop condition (stop bit), and ends read action. And this IC gets in standby status.
○Device addressing
・Output slave address after start condition from master.
・The significant 4 bits of slave address are used for recognizing a device type.
The device code of this IC is fixed to '1010'.
・The most insignificant bit (R / W --- READ/ WRITE ) of slave address is used for designating write or read action,
and is as shown below.
Setting R / W to 0 --- write (setting 0 to word address setting of random read)
Setting R / W to 1 --- read
Type
Slave address
BU9880GUL-W
1
0
1
0
0
0
0
R / W
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© 2010 ROHM Co., Ltd. All rights reserved.
2010.11 - Rev.A
7/16
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