291
CHAPTER 17 SERIAL INTERFACE (SIO3)
Remarks 1.
f
X
: main system clock oscillation frequency
2.
Figures in parentheses are for operation with f
X
= 8.38 MHz.
(2) Communication Operations
In the three-wire serial I/O mode, data is transmitted and received in 8-bit units. Each bit of data is sent or received
in synchronization with the serial clock.
The serial I/O shift register 30 (SIO30) is shifted in synchronization with the falling edge of the serial clock.
Transmission data is held in the SO30 latch and is output from the SO30 pin. Data that is received via the SI30
pin in synchronization with the rising edge of the serial clock is latched to SIO30.
Completion of an 8-bit transfer automatically stops operation of SIO30 and sets interrupt request flag (CSIIF30).
Figure 17-3. Timing of 3-Wire Serial I/O Mode
(3) Transfer start
A serial transfer starts when the following two conditions have been satisfied and transfer data has been set (or
read) to serial I/O shift register 30 (SIO30).
The SIO30 operation control bit (CSIE30) = 1
After an 8-bit serial transfer, either the internal serial clock is stopped or SCK30 is set to high level.
Transmit/transmit and receive mode
When CSIE30 = 1 and MODE0 = 0, transfer starts when writing to SIO30.
Receive-only mode
When CSIE30 = 1 and MODE0 = 1, transfer starts when reading from SIO30.
Caution
After data has been written to SIO30, transfer will not start even if the CSIE30 bit value is set
to “1”.
Completion of an 8-bit transfer automatically stops the serial transfer operation and interrupt request flag
(CSIIF30) is set.
SI30
DI7
DI6
DI5
DI4
DI3
DI2
DI1
DI0
CSIIF30
SCK30
1
SO30
DO7
DO6
DO5
DO4
DO3
DO2
DO1
DO0
2
3
4
5
6
7
8
Transfer completion
Transfer starts in synchronization with the SCK30 falling edge