8-Bit MCU,I/O type OTP MCU,1024x14 ROM,64x8 RAM,24-DIP,Holtek Operating voltage: fSYS=4MHz: 3.3V~5.5V fSYS=8MHz: 4.5V~5.5V 21 bidirectional I/O lines (max.) 1 interrupt input shared with an I/O line 8-bit programmable timer/event counter with overflow interrupt and 8-stage prescaler On-chip external crystal, RC oscillator and internal RC oscillator 32768Hz crystal oscillator for timing purposes only Watchdog Timer 102414 program memory ROM 648 data memory RAM