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Introduction. 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

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introduction
Introduction

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
what is a microcomputer
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

MPU

MCU

CLASSIFICATION

Device

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

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

System implementation

MCU

Multiple chips

Single chip

MPU

(Typically, only the CPUCore)

Memory

IO

Peripherals

CPUCore

Memory

Peripherals

I/O

Processor core (CPU)

32 bits or above

4, 8, 16, or 32 bits

Necessary for very complex, high performance and expandable systems

Needs external memory & peripherals to accomplish a task

Application considerations

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

Ideal for small, compact, and low-cost systems

Application examples

Handheld multimedia phone, car navigation system

Washing machine, rice cooker, air conditioner

Renesas product lines

SH-3 and SH-4 series

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

Differences Between MPUs and MCUs
typical mcu on chip functions

Main Clock

CPU(16-bit H8 type)

Sub-Clock

RAM

I/O

ROM

PWM

I/O

Output Port

PWM

Timer

I/O Port

I/O Port

Timer

Timer

I/O

I/O Port

Serial

Interface

Timer

I/O Port

Timer

WDT

I/O Port

ADC

LCDController

Input Port

Example: H8/38024 16-bit 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
processor core cpu

RISC

CISC

Instruction execution

Fast: 1 instruction/cycle

Slower: Many instructions take multiple cycles

Code efficiency

Lower: Moderate

High: Very compact code

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
  • 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

Memory Type

Mask ROM

PROM/OTP

Flash

DRAM

SRAM

Data

Retained?

Yes

Yes

Yes

No

No

Reprogram-mable?

No

No

Yes

Reads & writes, but temporary

storage only

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
clocks

Main Clock Circuit

MCU

OSC1 OSC2

Quartz

crystal

C1

C2

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
low power modes
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
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

MCU

Port Types

Input/Output

(SCI, I2C, etc.)

Input only

(ADC, etc.)

Output only

(DAC, LED drive, etc.)

timers and watchdog timer wdt

Watchdog Timer

Internal Reset Signal

Overflow

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
pulse width modulator pwm
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.

PWM Signals

PWM Output

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

adcs and dacs

Digitaloutput

ADC

Analoginput

Digitalinput

DAC

Analogoutput

(Serial [PWM]

or Parallel)

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
serial interface

CAN #1

CAN #2

CAN #3

CAN #4

X

CAN: a high-integrity, asynchronous serial data communication bus for automotive and industrial applications

Accept

Accept

Prepare

Select

Select

Select

Sendmessage

Receivemessage

Receivemessage

Receivemessage

CAN bus

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
bus controller

MCU

CPU

ExternalMemory

(DRAM)

RAM

ROM

Bus Controller

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
on chip debug ocd

Typical System Debug Setup

PC

OCD Emulator(Example: Renesas E8)

USB I/F

Target Board

MCU

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
    • Clock
other on chip functions

M16C/28

ADC

(AN0, AN1)

OSCD

Currents

3-phase

Motor

Control

Timer

IPM

BLDC

DCCT

Currents

ADC

(AN2, AN3)

INT0

Error

Pulse

PressureSensor

ADC

(AN6)

Hall Sensors

DMA

Timer A0

Pulse-width

Measurements

ADC

(AN7)

Bus-voltage

Sensor

INT3

INT4

I/Os

TimerA3

LEDs

INT5

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

basic embedded system signals

System Requirements

Application Needs

Debugging(Optional)

VCC

Clock

Inputs(keypad, sensors, switches, etc.)

Mode

MCU

Reset

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

Interrupts(Internal)

GND

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.)
what system developers want
What System Developers Want

1. Sufficient performance

2. Small code size

MCUs that meet the requirements of the application

3. Requisite peripherals

4. Low power consumption

5. Good EMC performance

6. Fail-safe features

7. Good Flash ROM technology

Support tools that shorten system development time

8. Good development environment

9. Complete set of SW/HW tools

course summary
Course Summary
  • 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