General Description
Introduction
The MC68HC908GR8 is a member of the low-cost, high-performance M68HC08 Family of 8-bit microcontroller units (MCUs). All MCUs in the family use the enhanced M68HC08 central processor unit (CPU08) and are available with a variety of modules, memory sizes and types, and package types.
This document also describes the MC68HC908GR4. The MC68HC908GR4 is a device identical to the MC68HC908GR8 except that it has less Flash memory. Only when there are differences from the MC68HC908GR8 is the MC68HC908GR4 specifically mentioned in the text.

Features
For convenience, features have been organized to reflect:
• Standard features of the MC68HC908GR8
• Features of the CPU08

Standard Features of the MC68HC908GR8
• High-performance M68HC08 architecture optimized for C-compilers
• Fully upward-compatible object code with M6805, M146805, and M68HC05 Families
• 8-MHz internal bus frequency
• FLASH program memory security(1)
• On-chip programming firmware for use with host personal computer which does not require high voltage for entry
• In-system programming
• System protection features:
   – Optional computer operating properly (COP) reset
   – Low-voltage detection with optional reset and selectable trip points for 3.0 V and 5.0 V operation
   – Illegal opcode detection with reset
   – Illegal address detection with reset
• Low-power design; fully static with stop and wait modes
• Standard low-power modes of operation:
   – Wait mode
   – Stop mode
• Master reset pin and power-on reset (POR)
• 7680 bytes of on-chip FLASH memory on the MC68HC908GR8 and 4096 bytes of on-chip FLASH memory on the MC68HC908GR4 with in-circuit programming capabilities of FLASH program memory
• 384 bytes of on-chip random-access memory (RAM)
• Serial peripheral interface module (SPI)
• Serial communications interface module (SCI)
• One 16-bit, 2-channel timer (TIM1) and one 16-bit, 1-channel timer (TIM2) interface modules with selectable input capture, output compare, and PWM capability on each channel
• 6-channel, 8-bit successive approximation analog-to-digital converter (ADC)
• BREAK module (BRK) to allow single breakpoint setting during in-circuit debugging
• Internal pullups on IRQ and RST to reduce customer system cost
• Clock generator module with on-chip 32-kHz crystal compatible PLL (phase-lock loop)
• Up to 21 general-purpose input/output (I/O) pins, including:
   – 19 shared-function I/O pins
   – Up to two dedicated I/O pins, depending on package choice
• Selectable pullups on inputs only on ports A, C, and D. Selection is on an individual port bit basis.
   During output mode, pullups are disengaged.
• High current 10-mA sink/10-mA source capability on all port pins
• Higher current 15-mA sink/source capability on PTC0–PTC1
• Timebase module with clock prescaler circuitry for eight user selectable periodic real-time interrupts with optional active clock source during stop mode for periodic wakeup from stop using an external 32-kHz crystal
• Oscillator stop mode enable bit (OSCSTOPENB) in the CONFIG register to allow user selection of having the oscillator enabled or disabled during stop mode
• 4-bit keyboard wakeup port
• 42-pin shrink dual in-line package (SDIP), 32-pin quad flat pack (QFP), 28-pin plastic dual-in-line package (DIP), or 28-pin small outline integrated circuit (SOIC)
• Specific features of the MC68HC908GR8 in 28-pin DIP and 28-pin SOIC are:
   – Port B is only 4 bits: PTB0–PTB3; 4-channel ADC module
   – No Port C bits

Features of the CPU08
Features of the CPU08 include:
• Enhanced HC05 programming model
• Extensive loop control functions
• 16 addressing modes (eight more than the HC05)
• 16-bit index register and stack pointer
• Memory-to-memory data transfers
• Fast 8 × 8 multiply instruction
• Fast 16/8 divide instruction
• Binary-coded decimal (BCD) instructions
• Optimization for controller applications
• Efficient C language support