
192
CHAPTER 12 SERIAL INTERFACE
User
’
s Manual U15017EJ2V0UD
Figure 12-4. Format of Serial Operation Mode Register 2
CSIE2
Enables or disables operation of SIO2
Shift register operation
Serial counter
Port
0
Stopped
Cleared
Port function
Note
1
Enabled
Count operation enabled
Serial function + port function
MODE2
Transfer operation mode flag
Operation mode
Transfer start trigger
SO2 output
0
Transmit or transmit/receive
mode
SIO2 write
Normal output
1
Receive mode
SIO2 read
Fixed to low level
SCL21
SCL20
Clock selection
0
0
External clock input to SCK2 pin
0
1
f
XX
/32 (131 MHz)
1
0
f
XX
/64 (65.5 kHz)
1
1
f
XX
/128 (32.7 kHz)
Note
The pins connected to SI2, SO2, and SCK2 can be used as port pins when CSIE2 = 0 (when the SIO2
operation is stopped).
Caution Because the SCK2 pin of serial interface 2 (SIO2) is an N-ch open-drain pin, the clock output
from this pin does not have a duty factor of 50% if the internal clock is selected.
The set values listed above are for clocks that can be used when a pull-up resistor of 10 k
is connected at f
XX
= 4.194 MHz.
Under any other conditions, or if the wiring capacitance of the board differs even when the
above conditions are satisfied, the operation may not be performed correctly even if the above
clock is selected. Be sure to perform evaluation before selecting a clock.
Remarks 1.
f
XX
: Main system clock frequency
2.
The values in parentheses are valid for operation when f
XX
is 4.194 MHz.
<7>
CSIE2
6
0
5
0
4
0
3
0
2
MODE2
1
SCL21
0
SCL20
Symbol
CSIM2
Address
FF92H
After reset
00H
R/W
R/W