Starter development plan of 8-bit MCU based on MC9RS08KB12 design

MC9RS08KB12/8/4/2 (RS08KB) is Freescale’s ultra-low-cost entry-level 8-bit MCU, which is easy to use, design flexibility and performance. RS08KB integrates a variety of peripherals and an efficient RS08 core, which supports interrupts, Improve system performance and save other component costs. RS08KB has up to 12KB flash memory, 256B RAM, high-resolution 12-channel 10-bit ADC, TPM, module timer and ACMP to provide block-speed precise detection and control. Target applications are small Home appliances, lighting control, low-end thermal control BLDC fans, handheld devices, battery chargers and toys. This article introduces the main features and block diagrams of MC9RS08KB12, as well as the main features and circuit diagrams of the DEMO9RS08KB12 demo board.

The MC9RS08KB12/8/4/2 (RS08KB) family includes ultra-low-cost, entry-level 8-bit MCUs that balance ease of use with design flexibility and performance. The RS08KB family has an integrated peripheral set which includes a highly efficient RS08 core that supports interrupt capability, helping to improve system performance and save additional components costs. The RS08KB family eases migration by offering multiple package and flash size options, along with pin compatibility with other 5V families as well as the CodeWarrior development tool to support other 8-bit families. The family is available in 20, 16 or 8-pin packages, and features up to 12 KB flash and 254B RAM, high-resolution 12-ch., 10-bit ADC, TPM, modulo timers and ACMP to provide fast, precise sensing and control.

Main features of MC9RS08KB12:

• 8-Bit RS08 Central Processor Unit (CPU)

– Up to 20 MHz CPU at 1.8 V to 5.5 V across temperature range of –40℃ to 85℃

– Subset of HC08 instruction set with added BGND instruction

– Single Global interrupt vector

• On-Chip Memory

– Up to 12 KB flash read/program/erase over full operating voltage and temperature, 12 KB/8 KB/4 KB/2 KB flash are optional

– Up to 254-byte random-access memory (RAM), 254-byte/126-byte RAM are optional

– Security circuitry to prevent unauthorized access to flash contents

• Power-Saving Modes

– Wait mode — CPU shuts down; system clocks continue to run; full voltage regulation

– Stop mode — CPU shuts down; system clocks are stopped; voltage regulator in standby

– Wakeup from power-saving modes using RTI, KBI, ADC, ACMP, SCI and LVD

• Clock Source Options

– Oscillator (XOSC) — Loop-control Pierce oscillator; crystal or ceramic resonator range of 31.25 kHz to 39.0625 kHz or 1 MHz to 16 MHz

– Internal Clock Source (ICS) — Internal clock source module containing a frequency-locked-loop (FLL) controlled by internal or external reference; precision trimming of internal reference allows 0.2% resolution and 2% deviation over temperature and voltage; supporting bus frequencies up to 10 MHz

• System Protection

– Watchdog computer operating properly (COP) reset with option to run from dedicated 1 kHz internal low power oscillator

– Low-voltage detection with reset or interrupt

– Illegal opcode detection with reset

– Illegal address detection with reset

– Flash-block protection

• Development Support

– Single-wire background debug interface

– Breakpoint capability to allow single breakpoint setting during in-circuit debugging

• Peripherals

– ADC — 12-channel, 10-bit resolution; 2.5 μs conversion time; automatic compare function; 1.7 mV/℃ temperature sensor; internal bandgap reference channel; operation in stop; hardware trigger; fully functional from 2.7 V to 5.5 V

– ACMP — Analog comparator; full rail-to-rail supply operation; option to compare to fixed internal bandgap reference voltage; can operate in stop mode

– TPM — One 2-channel timer/pulse-width modulator module; selectable input capture, output compare, or buffered edge- or center-aligned PWM on each channel

– IIC — Inter-integrated circuit bus module capable of operation up to 100 kbps with maximum bus loading; capable of higher baud rates with reduced loading

– SCI — One serial communications interface module with optional 13-bit break; LIN extensions

– MTIM — Two 8-bit modulo timers; optional clock sources

– RTI — One real-time clock with optional clock sources

– KBI — Keyboard interrupts; up to 8 ports

• Input/Output

– 18 GPIOs in 20-pin package; 14 GPIOs in 16-pin package; 6 GPIOs in 8-pin package; including one output-only pin and one input-only pin

– Hysteresis and configurable pullup device on all input pins; configurable slew rate and drive strength on all output pins

• Package Options


— 20-pin SOIC, 16-pin SOIC NB or TSSOP

– MC9RS08KB2

— 8-pin SOIC or DFN

MC9RS08KB12 target applications:

Small appliances

Lighting control

Simple logic replacements

Low-end thermal controlled BLDC fans

Hand-held devices

Battery chargers


Starter development plan of 8-bit MCU based on MC9RS08KB12 design

Figure 1. MC9RS08KB12 series block diagram

DEMO9RS08KB12 demo board

The 8-bit DEMO9RS08KB12 demonstration kit soldered with 20SOIC KB12, comes with everything required to complete an entire entry-level project using the RS08KB. The perfect solution that allows you to develop your next cost-effective application.

Main features of DEMO9RS08KB12 demo board:

MC9S08KB12, 20 SOIC

12K Bytes Flash

256 Bytes RAM

12Ch, 10-bit ADC

2-Ch, Timer/PWM

Internal Clock Source


Optional 32 kHz XTAL (not installed)

Integrated USB-BDM

BDM_PORT header for BDM cable support (not installed)

MCU_PORT socket header for access to MCU IO signals

On-board +5V regulator

Power Input Selection Jumpers

Power input from USB-BDM

Power input from Barrel connector and on-board regulator

Power Input from connector J1

Optional Power output through Connector J1

User Components Provided

Push Switches; 2 User, 1 Reset

LED Indicators; 2 User, VDD, D300

5K ohm POT w /LP Filter

Light Sensor w/ Amplifier


Power Select







40-pin MCU I/O Connector

2.0mm Barrel Connector

BDM_PORT (not installed)

USB Connectors

DB9 Connector
Starter development plan of 8-bit MCU based on MC9RS08KB12 design
Figure 2. Outline drawing of DEMO9RS08KB12 demo board

Figure 3. DEMO9RS08KB12 demo board circuit diagram

The Links:   R0878LS20K CM1000DUC-34SA