uPD789074 Subseries 8-Bit Single-Chip Microcontrollers UD - Home

CHAPTER 9 SERIAL INTERFACE 209.4.3 3-wire serial I/O modeThe 3-wire serial I/O mode is useful for connection of peripheral I/Os and display controllers, etc., that incorporatea conventional synchronous serial interface, such as the 75XL Series, 78K Series, 17K Series, etc.Communication is performed using three lines: the serial clock (SCK20), serial output (SO20), and serial input(SI20).(1) Register setting3-wire serial I/O mode settings are performed using serial operation mode register 20 (CSIM20),asynchronous serial interface mode register 20 (ASIM20), baud rate generator control register 20 (BRGC20),port mode register 2 (PM2), and port 2 (P2).(a) Serial operation mode register 20 (CSIM20)CSIM20 is set with a 1-bit or 8-bit memory manipulation instruction.RESET input clears CSIM20 to 00H.Symbol 6 5 4 3 2 1 0 Address After reset R/WCSIM20CSIE20 SSE20 0 0 DAP20 DIR20 CSCK20 CKP20FF72H 00H R/WCSIE203-wire serial I/O mode operation control0Operation disabled1Operation enabledSSE20SS20 pin selectionFunction of SS20/P23 pinCommunication status0Not usedPort functionCommunication enabled1Used0Communication enabled1Communication disabledDAP2001Outputs at the falling edge of SCK20.Outputs at the rising edge of SCK20.3-wire serial I/O mode data phase selectionDIR2001MSBLSBFirst-bit specificationCSCK2001External clock input to the SCK20 pinOutput of the dedicated baud rate generator3-wire serial I/O mode clock selectionCKP20013-wire serial I/O mode clock phase selectionClock is active low, and SCK20 is at high level in the idle state.Clock is active high, and SCK20 is at low level in the idle state.Caution Bits 4 and 5 must both be set to 0.140User’s Manual U14801EJ3V1UD