NEC 78014Y Series, User Manual

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CHAPTER 15 SERIAL INTERFACE CHANNEL 0 (
µ
PD78014 Subseries)
283
(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 the 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.
15.4.3 SBI mode operation
SBI (Serial Bus Interface) is a high-speed serial interface in compliance 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 microcontrollers 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 enables the application program
to control serial interface channel 0 to be simplified.
The SBI function is incorporated into various devices including 75X/XL Series devices and 78K Series.
Figure 15-11 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 (or 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) Cautions on SBI mode (d) described later when the SBI mode is used.