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CHAPTER 17 SERIAL INTERFACE CHANNEL 1
17.4 Operation of Serial Interface Channel 1
Serial interface channel 1 operates in the following three operation modes:
Operation stop mode
3-wire serial I/O mode
3-wire serial I/O mode with automatic transmit/receive function
17.4.1 Operation stop mode
Serial transfer is not executed in this mode. Consequently, the power consumption can be reduced. The serial
I/O shift register 1 (SIO1) can be used as an ordinary 8-bit register because it does not perform the sift operation.
In the operation stop mode, the P20/SI1, P21/SO1, P22/SCK1, P23/STB, and P24/BUSY pins can be used as
ordinary I/O port pins.
(1) Register setting
The operation stop mode is set by using the serial operation mode register 1 (CSIM1).
CSIM1 is set by using a 1-bit or 8-bit memory manipulation instruction.
This register is set to 00H when the RESET signal is input.
Notes 1.
These pins can be used freely as port pins.
2.
P20 (CMOS I/O) is used when only transmission is executed. Clear bit 7 (RE) of the automatic
data transmit/receive control register (ADCT) to 0.
Remark
×
PM
××
: Port mode register
P
××
: Output latch of port
: Don’t care
<7>
6
<5>
4
3
2
Symbol
1
0
FF68H
CSIM
10
CSIM1
CSIM
11
0
0
0
ATE
DIR
CSIE1
Address
On reset
R/W
00H
R/W
1
×
Note 2 Note 2
×
×
×
×
CSIE1
CSIM
11
P20 PM21 P21 PM22
Shift register
1 operation
SO1/P21
pin function
SCK1/P22
pin function
×
×
0
0
Note 1 Note 1
Operation
disabled
PM20
P22
Note 1 Note 1 Note 1
Note 1
×
0
1
0
1
0
1
1
×
Serial clock
count operation
control
SI1/P20
pin function
Cleared
P20
(CMOS I/O)
P21
(CMOS I/O)
P22
(CMOS I/O)
Operation
enabled
Count
operation
SI1
(input)
Note 2
SO1
(CMOS output)
SCK1
(input)
SCK1
(CMOS output)