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CHAPTER 18 SERIAL INTERFACE CHANNEL 1
18.4 Serial Interface Channel 1 Operations
The following three operating modes are available to the serial interface channel 1.
• Operation stop mode
• 3-wire serial I/O mode
• 3-wire serial I/O mode with automatic transmit/receive function
18.4.1 Operation stop mode
Serial transfer is not carried out in the operation stop mode. Thus, power consumption can be reduced. The serial
I/O shift register 1 (SIO1) does not carry out shift operation either, and thus it can be used as an ordinary 8-bit register.
In the operation stop mode, the P20/SI1, P21/SO1, P22/SCK1, P23/STB and P24/BUSY pins can be used as
ordinary input/output ports.
(1) Register setting
The operation stop mode is set with the serial operating mode register 1 (CSIM1).
CSIM1 is set with a 1-bit or 8-bit memory manipulation instruction.
RESET input sets CSIM1 to 00H.
Notes 1. Can be used freely as port function.
2. Can be used as P20 (CMOS input/output) when only transmitter is used (clear bit 7 (RE) of the
automatic data transmit/receive control register (ADTC) to 0).
Remark × : Don't care
PM×× : Port mode register
P×× : Port output latch
Operation
enable
6<5>43210<7>
Symbol
CSIM1 CSIE1 DIR ATE 0 0 0
CSIM11 CSIM10
SCK1
(Input)
CSIE1
0
FF68H 00H R/W
Address After Reset R/W
CSIM11
P20 PM21 P21 PM22
Note 2
Shift Register
1 Operation
Serial Clock Counter
Operation Control
SI1/P20 Pin
Function
SCK1/P22
Pin Function
×
1
0
1
0
× 00
1×
1
Note 1 Note 1
Note 1 Note 1
Count
operation
SI1
(Input)
×××××
Operation
stop
Clear P20 (CMOS
input/output)
P22 (CMOS
input/output)
×
PM20
SO1/P21 Pin
Function
SO1 (CMOS
output)
P21 (CMOS
input/output)
SCK1
(CMOS
output)
1
Note 1
Note 1
Note 2Note 2
P22
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