NEC PD78F9488 - Manual (Page 211)

CHAPTER 11 SERIAL INTERFACE 20
User’s Manual U15331EJ4V1UD
211
11.4.3 3-wire serial I/O mode
The 3-wire serial I/O mode is useful for connection of peripheral I/Os and display controllers, etc., which
incorporate a conventional clocked serial interface, such as the 75XL Series, 78K Series, and 17K Series.
Communication is performed using three lines: a serial clock (SCK20), serial output (SO20), and serial input
(SI20).
(1) Register
setting
3-wire serial I/O mode settings are performed using serial operation mode register 20 (CSIM20),
asynchronous serial interface mode register 20 (ASIM20), baud rate generator control register 20 (BRGC20),
port mode register 2 (PM2), and port 2 (P2).
(a) Serial operation mode register 20 (CSIM20)
CSIM20 is set with a 1-bit or 8-bit memory manipulation instruction.
RESET input sets CSIM20 to 00H.
CSIE20
0
1
3-wire serial I/O mode operation control
CSIE20 0 0 0 0 DIR20 CSCK20 0 CSIM20
Symbol Address After reset R/W
FF72H 00H R/W
<7> 6 5 4 3 2 1 0
Operation disabled
Operation enabled
DIR20
0
1
First-bit specification
MSB
LSB
CSCK20
0
1
3-wire serial I/O mode clock selection
External clock input to the SCK20 pin
Output of the dedicated baud rate generator
Cautions 1. Bits 0 and 3 to 6 must be set to 0.
2. When the external input clock is selected, set input mode by setting bit 0 of port
mode register 2 (PM2) to 1.
3. Switch operation modes after halting the serial transmission/reception operation.