406CHAPTER 18 SERIAL INTERFACE CHANNEL 118.4.2 3-wire serial I/O mode operationThe 3-wire serial I/O mode is valid for connection of peripheral I/O units and display controllers which incorporatea conventional synchronous serial interface such as the 75X/XL, 78K and 17K series.Communication is carried out with three lines of serial clock (SCK1), serial output (SO1) and serial input (SI1).(1) Register settingThe 3-wire serial I/O 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.Note If the external clock input has been selected with CSIM11 set to 0, set bit 1 (BUSY1) and bit 2 (STRB)of the automatic data transmit/receive control register (ADTC) to 0, 0.Remark ×: Don't careNotes 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 ADTCto 0).Remark × : Don't carePM×× : Port mode registerP×× : Port output latch6 <5> 4 3 2 1 0<7>SymbolCSIM1 CSIE1 DIR ATE 0 0 0 CSIM11 CSIM10CSIM1101Serial Interface Channel 1 Clock SelectionClock externally input to SCK1 pinNote8-bit timer register 2 (TM2) output1 Clock specified with bits 4 to 7 of timer clock select register 3 (TCL3)CSIM10×01FF68H 00H R/WAddress After Reset R/WATE01Serial Interface Channel 1 Operating Mode Selection3-wire serial I/O mode3-wire serial I/O mode with automatic transmit/receive functionDIR01Start BitMSBLSBSO1 Pin FunctionSI1/P20(Input)SO1 Pin FunctionSO1(CMOS output)OperationenableSCK1(Input)CSIE10CSIM11 P20 PM21 P21 PM22Note 2Shift Register 1OperationSerial Clock CounterOperation ControlSI1/P20 PinFunctionSCK1/P22Pin Function×1010× 0 01 ×1Note 1 Note 1 Note 1 Note 1CountoperationSI1(Input)× × × × × OperationstopClear P20 (CMOSinput/output)P22 (CMOSinput/output)×PM20 SO1/P21 PinFunctionSO1 (CMOSoutput)P21 (CMOSinput/output)SCK1(CMOSoutput)1Note 1Note 1Note 2Note 2P22
