CHAPTER 11 SERIAL INTERFACE FUNCTION
User’s Manual U15109EJ3V0UD
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11.5.4 I
2
C bus definitions and control methods
The following section describes the I
2
C bus’s serial data communication format and the signals used by the I
2
C
bus. The transfer timing for the “start condition”, “data”, and “stop condition” output via the I
2
C bus’s serial data bus is
shown below.
Figure 11-24. I
2
C Bus Serial Data Transfer Timing
1 to 7
8
9
1 to 7
8
9
1 to 7
8
9
SCL
SDA
Start
condition
Address
R/W
ACK
Data
Data
Stop
condition
ACK
ACK
The master device outputs the start condition, slave address, and stop condition.
The acknowledge signal (ACK) can be output by either the master or slave device (normally, it is output by the
device that receives 8-bit data).
The serial clock (SCLn) is continuously output by the master device. However, in the slave device, the SCLn’s
low-level period can be extended and a wait can be inserted (n = 0, 1).
(1) Start condition
A start condition is met when the SCLn pin is high level and the SDAn pin changes from high level to low level.
The start conditions for the SCLn pin and SDAn pin are signals that the master device outputs to the slave
device when starting a serial transfer. The slave device includes hardware for detecting start conditions (n = 0,
1).
Figure 11-25. Start Conditions
H
SCLn
SDAn
A start condition is output when bit 1 (STTn) of IIC control register n (IICCn) is set to 1 after a stop condition has
been detected (SPDn: Bit 0 = 1 in IIC status register n (IICSn)). When a start condition is detected, IICSn’s bit 1
(STDn) is set to 1 (n = 0, 1).