CHAPTER 3 PIN FUNCTIONSUser’s Manual U14826EJ5V0UD363.2 Description of Pin Functions3.2.1 P00 to P07 (Port 0)These pins constitute an 8-bit I/O port and can be set to input or output port mode in 1-bit units by using port moderegister 0 (PM0).3.2.2 P20, P21 (Port 2)These pins constitute a 2-bit I/O port. In addition, these pins function as the timer input/output and bit sequentialbuffer output.Port 2 can be set to the following operation modes in 1-bit units.(1) Port modeIn port mode, P20 and P21 function as a 2-bit I/O port. Port 2 can be set to input or output port mode in 1-bitunits by using port mode register 2 (PM2).(2) Control modeIn this mode, P20 and P21 function as the timer input/output and the bit sequential buffer output.(a) BSFOThis is the output pin of the bit sequential buffer.(b) TMIThis is the external clock input pin for the timer 40.(c) TMOThis is the output pin of the timer 40.3.2.3 P40 to P43 (Port 4)These pins constitute a 4-bit input-only port. In addition, these pins function as the key return input.(1) Port modeIn port mode, P40 to P43 function as a 4-bit input-only port. For mask ROM versions, an on-chip pull-upresistor can be specified by means of the mask option.(2) Control modeIn this mode, P40 to P43 function as the key return input (KR10 to KR13).3.2.4 RESETAn active-low system reset signal is input to this pin.3.2.5 X1, X2 (μPD789860 Subseries)These pins are used to connect a crystal resonator for system clock oscillation.To supply an external clock, input the clock to X1 and input the inverted signal to X2.3.2.6 CL1, CL2 (μPD789861 Subseries)These pins are used to connect a resistor (R) and capacitor (C) for system clock oscillation.To supply an external clock, input the clock to CL1 and input the inverted signal to CL2.
