425CHAPTER 19 SERIAL INTERFACE CHANNEL 119.4 Serial Interface Channel 1 OperationsThe 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 function19.4.1 Operation stop modeSerial transfer is not carried out in the operation stop mode. Thus, power consumption can be reduced. Theserial I/O shift register 1 (SIO1) does not carry out shift operation either, and thus it can be used as an ordinary8-bit register.In the operation stop mode, the P20/SI1, P21/SO1, P22/SCK1, P23/STB, and P24/BUSY pins can be used asordinary input/output ports.(1) Register settingThe 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 (set bit 7 (RE) of theautomatic data transmit/receive control register (ADTC) to 0).Remark x : Don’t carePMxx : Port mode registerPxx : Port output latchOperationenable6 <5> 4 3 2 1 0<7>SymbolCSIM1 CSIE1 DIR ATE 0 0 0 CSIM11 CSIM10SCK1(Input)CSIE10FF68H 00H R/WAddress After Reset R/WCSIM11P20 PM21 P21 PM22Note 2Shift Register1 OperationSerial Clock CounterOperation ControlSI1/P20 PinFunctionSCK1/P22Pin Functionx1010x 0 01 x1Note 1 Note 1 Note 1 Note 1CountoperationSI1(Input)x x x x x OperationstopClear P20 (CMOSinput/output)P22 (CMOSinput/output)xPM20 SO1/P21 PinFunctionSO1 (CMOSoutput)P21 (CMOSinput/output)SCK1(CMOSoutput)1Note 1Note 1Note 2Note 2P22
