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4.2 Explanation of Operation
2
4.2.1 I
C bus function
(a)
Start conditions
A start condition is met when the SCL pin is at high level (a serial clock has not been output) and the SDA pin
changes from high level to low level.
A start condition is a signal that the master device outputs to the slave device when starting a serial transfer.
2
This I
C bus only supports the slave function.
(b)
Slave ID
The slave ID is defined by the 7 bits of data that follow the start condition.
This slave ID is used to select a specific slave out of several slaves connected to a bus line. Normally, one
slave ID is assigned to one slave. Since the
(control register) and LCDSEG (display memory) can be selected as access targets.
A slave detects via hardware that data on the SDA line is a slave ID, and checks whether the 7-bit data
matches the slave ID (0111000 or 0111001 in the
µ
the
PD71312 is selected and communicates with the master device until the master device transmits a start
condition or stop condition.
SCL
SDA
2
CHAPTER 4 I
C COMMUNICATIONS
Figure 4-2. Start Conditions
H
SCL
SDA
µ
PD71312 has two internal slave IDs, however, LCDCTL
µ
PD71312). If the 7-bit data matches the slave ID values,
Figure 4-3. Slave ID
1
2
3
4
5
ID6
ID5
ID4
ID3
ID2
Slave ID
User's Manual U18438EJ2V0UD
6
7
8
9
ID1
ID0
R/W
51
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