CHAPTER 11 SERIAL INTERFACE FUNCTION
User’s Manual U15109EJ3V0UD
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(2) 3-wire serial I/O mode
3-wire serial I/O mode is useful when connecting to devices such as peripheral I/O that include a clocked serial
interface, and display controllers.
This mode executes data transfers via three lines: a serial clock line (SCK4), a serial output line (SO4), and a
serial input line (SI4).
(a) Register settings
3-wire serial I/O mode is set by the variable-length serial control register 4 (CSIM4).
Figure 11-8. CSIM4 Setting (3-Wire Serial I/O Mode)
After reset:
00H
R/W
Address: FFFFF2E2H
<7>
6
5
4
3
2
1
0
CSIM4
CSIE4
0
0
0
0
MODE4
0
SCL4
SIO4 operation enable/disable specification
CSIE4
Shift register operation
Serial counter
Port
1
Operation enabled
Count operation enabled
Serial fu port function
Transfer operation mode flag
MODE4
Operation mode
Transfer start trigger
SO4 output
0
Transmit/receive mode
Write to SIO4
Normal output
1
Receive-only mode
Read from SIO4
Port function
SCL4
Clock selection
0
External clock input (SCK4)
1
BRG (Baud rate generator)