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CHAPTER 15 SERIAL INTERFACE SIO3
15.1 SIO3 Functions
The serial interface SIO3 has the following two modes.
(1) Operation stop mode
This mode is used when serial transfers are not performed. For details, see 15.4.1 Operation stop mode.
(2) 3-wire serial I/O mode (fixed as MSB first)
This is an 8-bit data transfer mode using three lines: a serial clock line (SCK), serial output line (SO), and serial
input line (SI).
Since simultaneous transmit and receive operations are enabled in 3-wire serial I/O mode, the processing time
for data transfers is reduced.
The first bit in the 8-bit data in serial transfers is fixed as the MSB.
3-wire serial I/O mode is useful for connection to a peripheral I/O device that includes a clock-synchronous serial
interface, a display controller, etc. For details, see 15.4.2 Three-wire serial I/O mode.
Figure 15-1 shows the SIO3 block diagram.
Figure 15-1. SIO3 Block Diagram
Internal bus
Internal bus
Selector
Serial I/O shift
register (SIO)
Serial clock
counter
Serial clock control
circuit
INTCSI
Serial operation mode register (CSIM)
2
SI/P52
SO/P51
SCK/P50
CSIE MODE SCL1 SCL0
f
X
/2
2
f
X
/2
3
f
X
/2
4
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