Purpose – This course introduces basic facts about microcontrollers.

Objectives – Understand the differences between microcontrollers (MCUs) and

microprocessors (MPUs)– Obtain an overview of on-chip functions and basic system signals– Learn about the typical questions engineers ask when choosing MCUs

for new embedded system designs

Content– 19 pages

Learning Time– 25 minutes

Introduction

What is a Microcomputer?

• General definition: Small computer capable of performing specific tasks

– Examples of tasks: controlling operation and functions of alarm systems, power tools, digital cameras, traffic signals, etc.

– Acts as “brain” of an embedded system, executing functions according to stored instructions (application software)

• More-specific definition: Computer chip with Central Processing Unit (CPU)

– Two classifications

• Microprocessor unit (MPU)

• Microcontroller unit (MCU)

Differences Between MPUs and MCUs

System implementation

Handheld multimedia phone, car navigation system

Application examples

SH-3 and SH-4 seriesRenesas product lines

32 bits or aboveProcessor core (CPU)

Necessary for very complex, high performance and expandable systems

Needs external memory & peripherals to accomplish a task

Application considerations

Typically contains only the main processor (CPU core) — no memory for program storage

Device

MPUCLASSIFICATION

MPU(Typically, only the

CPUCore)

Memory

Peripherals

IO

Multiple chips

Washing machine, rice cooker, air conditioner

M16C, H8, SH-1, and SH-2 series

4, 8, 16, or 32 bits

Self-contained to complete a task with no/few external components

Ideal for small, compact, and low-cost systems

Contains CPU core, memory, peripherals, and I/O integrated

MCU

CPUCore

Memory

Peripherals

I/O

Single chip MCU

Typical MCU On-chip Functions

• CPU• Memory (RAM and ROM)• Clock(s)• Low-power Modes• Input/Output Ports• Timers & Watchdog Timer (WDT)• Pulse Width Modulator (PWM)• Analog-to-Digital Converter (ADC)• Serial Interface• Bus Controller• On-chip Debug• Other

CPU(16-bit H8 type)Main Clock

Sub-Clock RAM

ROM

Timer

Timer

Timer

Timer

WDTTimer

ADCLCD

Controller

Serial Interface

PWM

PWM

I/O P

ort

Example: H8/38024 16-bit MCU

I/O P

ort

Inp

ut

Po

rt

I/OI/O

Po

rtI/O

I/O P

ort

I/O P

ort

Ou

tpu

t P

ort

I/O

Processor Core (CPU)

• Function– Fetches and executes machine code – Provides levels of code efficiency and performance

• Architectural design features– CISC type or RISC type

• RISC has fewer instructions– Word size: 4, 8, 16, or 32 bits– Arithmetic Logic Unit for arithmetic and floating point operations– General registers for data processing and temporary storage– Special registers (program counter, stack, conditional, status)

to assist in program control– Data bus for interconnections– Operating frequency/clock speed range Voltage dependent

RISC

CISC

Instruction execution

Fast: 1 instruction/cycle

Slower: Many instructions take multiple cycles

Code efficiency

Lower: Moderate

High: Very compact code

Measuring CPU performance• MIPS (million instructions per second)

- Number of machine instructions that a computer can execute in one second- Benchmark tests provide only a rough indication of performance- Ultimate test is how well the MCU or MPU performs in the actual application

Memory (ROM/RAM)

• ROM (Read Only Memory) = Non-volatile – Used for program and fixed data storage– Contents retained when power is turned off– Size: from 1KB to 512KB and more– Examples:

• Mask ROM• Programmable Read-Only Memory (PROM),

also called One-Time Programmable (OTP)• Flash ROM (reprogrammable)

• RAM (Random Access Memory) = Volatile– Used for temporary data storage – Contents lost when power is turned off– Size: from 256 bytes to 48KB or more– Examples:

• Dynamic RAM (DRAM) — needs refresh• Static RAM (SRAM) — uses less power• Other: Cache — tightly coupled to CPU

of high-performance MPUs/MCUs

Memory Type

Mask ROM

PROM/OTP

Flash

DRAM

SRAM

Data Retained?

Yes

Yes

Yes

No

No

Reprogram-mable?

No

No

YesReads & writes,

but temporarystorage only

Clocks

• Essential for MCU operation • Typically there are two clocks

- Main clock • Drives CPU and controls its operation• Can be divided or multiplied for slower or faster

operating speed• External design uses crystal and two capacitors• Internal design built with modern technology produces

40MHz with 1% accuracy; saves cost, simplifies design

- Sub-clock• Generates a second (lower) frequency that drives CPU

in a slower, low-power mode (Standby mode, etc.) • Also used for driving some peripheral functions• Typically a 32.768kHz clock that enables accurate

generation of a second frequency via a 16-bit counter

OSC1 OSC2

MCU

Quartzcrystal

C1 C2

Main Clock Circuit

Low-power Modes

• Required for portable devices that achieve extended operating time on battery power, as well as many other energy-efficient products

• Reduce power consumption by various means

– Running at slower speed, such as sub clock (32.768kHz)• Sleep, Sub-active, Standby modes

– Shutting off unused peripherals• Module Stop mode

In some of the latest MCUs, Standby mode consumes <1µA

Ports: I/O, Input and Output

Interface to the “outside world”

• I/O ports monitor and control communication between devices

– Can be parallel or serial

• Input-only ports acquire data from external sensors, etc.

• Output-only ports drive external displays and actuators, etc.

– High-current (20mA) port • Drives an LED directly

– Open-collector/drain port• Interfaces with higher-level supply

circuitry• Implements wired-NOR condition

MCUPort Types

Output only(DAC, LED drive, etc.)

Input only(ADC, etc.)

Input/Output(SCI, I2C, etc.)

Timers and Watchdog Timer (WDT)

• Count clock pulses to control sequences of events or processes

• Timers (8-bit or 16-bit)

– Measure timing of events or generate output signals– Have various operating modes and features for different applications– Can be cascaded to create larger timers

• WDT (Watchdog Timer)

– Safeguards MCU by providing safe exit from a malfunctioning program– Must be reset at regular intervals or reset/restart will be generated

ResetControl

Internal Reset Signal

ITI (interruptrequest signal)

WDTOVFClock

Internal Clock Sources

WTCNTOverflow

Clock Select

WTSCR

BusI/F Module bus

Internal bus

InterruptControl

WRCSR

ResetControl

Internal Reset Signal

ITI (interruptrequest signal)

WDTOVFClock

Internal Clock Sources

WTCNTOverflow

Clock Select

WTSCR

BusI/F Module bus

Internal bus

InterruptControl

WRCSR

Watchdog TimerInternal Reset Signal

Overflow

Pulse Width Modulator (PWM)

• Generates continuous pulses at preset intervals

• Width of pulse can be set and varied in response to a control signal

• Can be used to drive a motor, light an LED, change power level, etc.

Control signal sets nominal width of PWM output pulse and causes it to vary

PWM Output

PWM Signals

ADCs and DACs

Provide interfaces to the analog (real) world

• Analog-to-digital converter (ADC or A/D)

– Converts analog signal levels to digital values– Important characteristics

• Accuracy and Resolution (determined by number of bits: 10, 12, 14…)

• Sampling frequency• Conversion technology (successive

approximation, delta-sigma, etc.)

• Digital-to-analog converter (DAC or D/A)

– Converts digital values to analog signal levels– Can be improvised using a low-pass filter

after a PWM output

ADC

Analoginput

Digitaloutput

DAC

(Serial [PWM]or Parallel)

Analogoutput

Digitalinput

Serial Interface

• Connects MCU to other parts of embedded system or to other systems

• Various types

– Asynchronous mode (most widely used)

– Synchronous mode (has higher transfer rate)

– Other examples: USB, I2C, SPI, LIN, CAN • Based on industry standards• Optimized for certain applications

• Generally uses only 3 pins

– Serial In, Serial Out, and Clock

Accept

Select

Receivemessage

CAN bus

Accept

Select

Receivemessage

Prepare

Sendmessage

Receivemessage

Select

X

CAN #1 CAN #2 CAN #3 CAN #4

CAN: a high-integrity, asynchronous serial data communication

bus for automotive and industrial applications

Bus Controller

• Incorporated in MCUs that must access external memory as well as internal memory

• Manages internal and external memory buses

• Controls bus communication functions– Refresh for DRAM – Length of wait states– Bus arbitration– Other signal-control tasks

Bus Controller

CPU

RAM

ROM

MCU

ExternalMemory(DRAM)

On-Chip Debug (OCD)

• Circuitry incorporated in MCU for system development and debugging

• JTAG interface commonly used (No standard for JTAG debugging)

• Debugger (typically purchased from MCU manufacturer or custom built)

• Usually requires only a few device pins to implement MCU control via a “JTAG-like” emulator on a PC

– Mode selection

– Data in/out

– ClockUSB I/F

PC

Target Board

OCD Emulator (Example: Renesas E8)

MCU

Typical System Debug Setup

Other On-chip Functions

• Many other peripherals can be integrated to perform specific tasks

– LCD controller, power-line communication (PLC), Ethernet MAC, 3-phase motor control timer, DMA, and more

• Additional functions enhance fail-safe design of embedded systems

– Low-voltage detection (LVD), power-on reset (POR), oscillation-stop detection (OSD)

Application example: MCU control of brushless DC motor

Timer A0

ADC(AN0, AN1)

I/OsTimer

A3

INT3

INT4

INT5

BLDC

INT0

3-phaseMotor

Control Timer

Hall Sensors

Pulse-widthMeasurements

ErrorPulse

OSCDCurrents

DCCTCurrents

PressureSensor

Bus-voltageSensor

ADC(AN2, AN3)

ADC(AN6)

ADC(AN7)

LEDs

IPM

M16C/28

DMA

Basic Embedded System Signals

• Required for MCU/system operation

– Power (VCC & GND), Clock, Mode, Reset, and Debugging (optional)

• Used by application

– Inputs (keypad, switches, sensor data, network communication, etc.)– Outputs (motor control, LCD drive, network communication,

actuator energization, etc.)

ClockModeReset

VCC

Debugging(Optional)

Outputs(Control signals, display drive, actuator drives, etc.)

Inputs(keypad, sensors, switches, etc.)

System Requirements Application Needs

GND

MCU

Interrupts(Internal)

What System Developers Want

8. Good development environmentSupport tools that

shorten system development time

2. Small code size

1. Sufficient performance

3. Requisite peripherals

4. Low power consumption

5. Good EMC performance

6. Fail-safe features

7. Good Flash ROM technology

MCUs that meet the requirements of the application

9. Complete set of SW/HW tools

• Differences between MCUs and MPUs

• Functions within an MCU

• Basic embedded system signals

• Questions engineers ask when choosing an MCU

For more information, please visit our Web site:www.renesas.com

Course Summary