CHAPTER 10 SERIAL INTERFACE FUNCTION
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10.3.4 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. Figure 10-13 shows the transfer timing for the “start condition”, “data”, and “stop condition” output via the I
2
C
bus’s serial data bus.
Figure 10-13. I
2
C Bus’s Serial Data Transfer Timing
1-7
8
9
1-7
8
9
1-7
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 (SCL) is continuously output by the master device. However, in the slave device, the SCL’s low
level period can be extended and a wait can be inserted.
(1)
Start condition
A start condition is met when the SCL pin is at high level and the SDA pin changes from high level to low level.
The start conditions for the SCL pin and SDA 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.
Figure 10-14. Start Conditions
H
SCL
SDA
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