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CHAPTER 13
SERIAL INTERFACE SIO0
User’s Manual U12790EJ2V0UD
(a) Start condition
When the SDA0 (SDA1) pin level is changed from high to low while the SCL pin is high, this transition
is recognized as the start condition signal. This start condition signal, which is created using the SCL
and SDA0 (or SDA1) pins, is output from the master device to slave devices to initiate a serial transfer.
Refer to 13.4.6 Cautions on use of I2C bus mode, for details of the start condition output.
The start condition signal is detected by hardware incorporated in slave devices.
Figure 13-37. Start Condition
(b) Address
The 7 bits following the start condition signal are defined as an address.
The 7-bit address data is output by the master device to specify a specific slave from among those
connected to the bus line. Each slave device on the bus line must therefore have a different address.
Therefore, after a slave device detects the start condition, it compares the 7-bit address data received
and the data of slave address register 0 (SVA0). After the comparison, only the slave device in which
the data matches becomes the communication partner, and subsequently performs communication with
the master device until the master device sends a start condition or stop condition signal.
Figure 13-38. Address
(c) Transfer direction specification
The 1 bit that follows the 7-bit address data sent from the master device, is defined as the transfer direction
specification bit. If this bit is 0, it is the master device which will send data to the slave. If it is 1, it is
the slave device which will send data to the master.
Figure 13-39. Transfer Direction Specification
H
SCL
SDA0 (SDA1)
1
2
3
456
7
A6
A5
A4
A3
A2
A1
A0
R/W
Address
SCL
SDA0 (SDA1)
2
3
456
7
A6
A5
A4
A3
A2
A1
A0
R/W
Transfer direction
specification
SCL
8
1
SDA0 (SDA1)