
197
CHAPTER 12 SERIAL INTERFACE
User
’
s Manual U15017EJ2V0UD
(2) Communication operation
In the three-wire serial I/O mode, data is transmitted or received in 8-bit units. Each bit of the data is transmitted
or received in synchronization with the serial clock.
The shift operation of serial I/O shift register n (SIOn) is performed in synchronization with the falling of the serial
clock (SCKn). The transmit data is retained by the SOn latch and output from the SOn pin. At the rising edge
of SCKn, the receive data input to the SIn pin is latched to SIOn.
When transfer of 8-bit data has been completed, SIOn automatically stops its operation, and an interrupt
request flag (CSIIFn) is set.
Figure 12-5. Timing in 3-Wire Serial I/O Mode
Remark
n = 0 to 2
(3) Transfer start
Serial transfer is started when data is assigned to (or read from) serial I/O shift register n (SIOn) if the following
two conditions are satisfied.
Operation control bit of SIOn (CSIEn) = 1
If the internal serial clock is stopped or SCKn is high after 8-bit serial transfer
Transmit or transmit/receive mode
Transfer is started if SIOn is written when CSIEn = 1 and MODEn = 0.
Receive mode
Transfer is started if SIOn is read when CSIEn = 1 and MODEn = 1.
Caution Transfer is not started even if CSIEn is set to 1 after data has been written to SIOn.
Serial transfer is automatically stopped and an interrupt request flag (CSIIFn) is set when 8-bit transfer has
been completed.
Remark
n = 0 to 2
SCKn
SIn
SOn
CSIIFn
Transfer is started at falling edge of SCKn
Transfer completed
1
2
3
4
5
6
7
8
DI7
DI6
DI5
DO7
DO6
DO5
DI4
DI3
DI2
DO4
DO3
DO2
DI1
DI0
DO1
DO0