Three-Wire Serial I/O Mode - NEC mPD780973 Series Preliminary User's Manual

15.4.2 Three-wire serial I/O mode

The three-wire serial I/O mode is useful when connecting a peripheral I/O device that includes a clock-synchronous
serial interface, a display controller, etc.
This mode executes data transfers via three lines: a serial clock line (SCK), serial output line (SO), and serial input
line (SI).
(1) Register settings
3-wire serial I/O mode is set via serial operation mode register (CSIM).
CSIM is set with a 1-bit or 8-bit memory manipulation instruction.
The RESET input resets the value to 00H.
Caution In the 3-wire serial I/O mode, set the port mode register (PM5X) as follows. Besides that,
set all output latches to 0.
• When serial clock output (Master transmit or Master receive)
Set P50 (SCK) to the output mode (PM50 = 0)
• When serial clock input (Slave transmit or Slave receive)
Set P50 to the input mode (PM50 = 1)
• When transmit/transceive mode
Set P51 (SO) to the output mode (PM51 = 0)
• When receive mode
Set P52 (SI) to the input mode (PM52 = 1)
Figure 15-4. Serial Operation Mode Register (CSIM) Format
Address: FF84H After Reset: 00H
Symbol 7
CSIM CSIE
CSIE
0
1
MODE
0
1
SCL1
0
0
1
1
Caution Bits 3 to 6 must be set to 0.
CHAPTER 15 SERIAL INTERFACE SIO3
R/W
6 5
0 0
SIO3 Operation Enable/Disable Specification
Operation disable
Operation enable
Transfer Operation Mode Flag
Transmit or transmit/receive mode
Receive-only mode
SCL0
0 External clock input
2
1 f /2
X
3
0 f /2
X
4
1 f /2
X
4 3 2
0 0 MODE
Shift Register Operation
Operation Mode
Clock Selection (f = 8.38 MHz)
X
1 0
SCL1 SCL0
187