NEC 78014Y Series, User Manual

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CHAPTER 16 SERIAL INTERFACE CHANNEL 0 (
µ
PD78014Y Subseries)
378
16.4.5 I
2
C bus mode operation
The I
2
C bus mode is used when communication operations are performed between a single master device and
multiple slave devices. This mode configures a serial bus that includes only a single master device, and is based
on the clocked serial I/O format with the addition of bus configuration functions, which allows the master device to
communicate with a number of (slave) devices using only two lines: serial clock (SCL) line and serial data bus (SDA0
or SDA1) line. Consequently, when the user plans to configure a serial bus which includes multiple microcontrollers
and peripheral devices, using this configuration results in reduction of the required number of port pins and on-board
wires.
In the I
2
C bus specification, the master sends start condition, data, and stop condition signals to slave devices
through the serial data bus.
Slave devices automatically detect and distinguish the type of signals due to the signal detection function
incorporated as hardware. This simplifies the application program to control I
2
C bus.
An example of a serial bus configuration is shown in Figure 16-36. This system below is composed of CPUs and
peripheral ICs having serial interface hardware that complies with the I
2
C bus specification.
Note that pull-up resistors are required to connect to both serial clock line and serial data bus line, because open-
drain buffers are used for the serial clock pin (SCL) and the serial data bus pin SDA0 (SDA1) on the I
2
C bus.
The signals used in the I
2
C bus mode are described in Table 16-6.
Figure 16-36. Serial Bus Configuration Example Using I
2
C Bus
SCL
SDA0 (SDA1)
SCL
SDA0 (SDA1)
SCL
SDA0 (SDA1)
SCL
SDA
Slave CPU1
Master CPU
V
DD
Slave CPU2
Slave IC
V
DD
Serial Clock
Serial Data Bus