CHAPTER 13 SERIAL INTERFACE CHANNEL 0
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User’s Manual U11302EJ4V0UM
(5) Transfer start
Serial transfer is started by setting transfer data to serial I/O shift register 0 (SIO0) when the following
two conditions are satisfied.
•
Serial interface channel 0 operation control bit (CSIE0) = 1
•
Internal serial clock is stopped or SCK0 is at high level after 8-bit serial transfer.
Caution If CSIE0 is set to “1” after data write to SIO0, transfer does not start.
Upon termination of 8-bit transfer, serial transfer automatically stops and the interrupt request flag
(CSIIF0) is set.
13.4.3 SBI mode operation
SBI (Serial Bus Interface) is a high-speed serial interface that complies with the NEC Electronics serial bus
format.
SBI is a single-master high-speed serial bus with a format in which a bus configuration function has been
added to the clocked serial I/O method so that it can carry out communication with two or more devices using
two signal lines. Thus, when configuring a serial bus with two or more microcontrollers or peripheral ICs, the
number of ports to be used and the number of wires on the board can be decreased.
The master device can output to the serial data bus of the slave device “addresses” for selection of the serial
communication target device, “commands” to instruct the target device and actual “data”. The slave device can
identify the received data as an “address”, “command”, or “data”, by hardware. This function can simplify the
application program which controls serial interface channel 0.
The SBI function is incorporated into various devices including the 75XL Series and 78K Series.
Figure 13-9 shows a serial bus configuration example when a CPU having a serial interface compliant with
SBI and peripheral ICs are used.
In SBI, the SB0 (SB1) serial data bus pin is an open-drain output and so the serial data bus line is in a wired-
OR state. A pull-up resistor is therefore necessary for the serial data bus line.
Refer to
(11) SBI mode precautions (d)
described later when the SBI mode is used.
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