CHAPTER 14 SERIAL INTERFACE CHANNEL 0
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(5) Transfer start
Serial transfer is started by setting transfer data to the 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 a 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.
14.4.3 SBI mode operation
SBI (Serial Bus Interface) is a high-speed serial interface that complies with the NEC serial bus format.
SBI has a format with the bus configuration function added to the clocked serial I/O method so that it can carry
out communication with two or more devices with two signal conductors on the single-master high-speed serial
bus. Thus, when making up a serial bus with two or more microcomputers and 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 into “address”, “command” or “data”, by hardware. This function helps simplify the
application program that controls serial interface channel 0.
The SBI function is incorporated into various devices including 75X/XL-Series 78K-Series devices.
Figure 14-9 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 serves for open-drain output and so the serial data bus line is in
wired-OR state. A pull-up resistor is necessary for the serial data bus line.
Refer to
(11) SBI mode precautions (d)
described later when the SBI mode is used.