323CHAPTER 16 SERIAL INTERFACE CHANNEL 0 (μPD78058F SUBSERIES)(5) Pin configurationThe serial clock pin SCK0 and serial data bus pin SB0 (SB1) have the following configurations.(a) SCK0 ............ Serial clock input/output pin<1> Master .. CMOS and push-pull output<2> Slave .... Schmitt input(b) SB0 (SB1) .... Serial data input/output dual-function pinBoth master and slave devices have an N-ch open drain output and a Schmitt input.Because the serial data bus line has an N-ch open-drain output, an external pull-up resistor is necessary.Figure 16-26. Pin ConfigurationCaution When receiving data, it is necessary to set the N-ch open drain output in the high impedancestate, so please write FFH in serial I/O shift register 0 (SIO0) in advance. This will keep itin the high impedance state at all times during transmission. However, in the case of thewake up function instruction bit (WUP) = 1, the N-ch open drain output is always in the highimpedance state, so it is not necessary to write FFH in SIO0 before reception.SI0SO0SI0SO0(Clock Input)Clock OutputMaster DeviceClock Input(Clock Output)Serial ClockSCK0 SCK0RLSerial Data BusSB0 (SB1) SB0 (SB1)N-ch Open-Drain N-ch Open-DrainSlave DeviceAVDDAVSS AVSS
