General Description
The Enhanced I/O MCUs are a series of 8-bit high performance, RISC architecture microcontrollers specifically designed for a wide range of applications. The usual Holtek microcontroller features of low power consumption, I/O flexibility, timer functions, oscillator options, power down and wake-up functions, watchdog timer and low voltage reset, combine to provide devices with a huge range of functional options while still maintaining a high level of cost effectiveness. The fully integrated system oscillator HIRC, which requires no external components and which has three frequency selections, opens up a huge range of new application possibilities for these devices, some of which may include industrial control, consumer products, household appliances subsystem controllers, etc.

Features
CPU Features
• Operating voltage:
   fSYS = 4MHz: 2.2V~5.5V
   fSYS = 8MHz: 3.3V~5.5V
   fSYS = 12MHz: 4.5V~5.5V
• Up to 0.33μs instruction cycle with 12MHz system clock at VDD= 5V
• Oscillator types:
   External high freuency Crystal -- HXT
   External RC -- ERC
   Internal RC -- HIRC
   External low frequency crystal -- LXT
• Three operational modes: Normal, Slow, Sleep
• Fully integrated internal 4MHz, 8MHz and 12MHz oscillator requires no external components
• Watchdog Timer function
• LIRC oscillator function for watchdog timer
• All instructions executed in one or two instruction cycles
• Table read instructions
• 63 powerful instructions
• Up to 6-level subroutine nesting
• Bit manipulation instruction
• Low voltage reset function
• Wide range of available package types

Peripheral Features
• Up to 26 bidirectional I/O lines
• Software controlled 4-SCOM lines LCD driver with 1/2 bias
• External interrupt input shared with an I/O line
• Up to three 8-bit programmable Timer/Event Counter with overflow interrupt and prescaler
• Time-Base function
• Programmable Frequency Divider -- PFD