1. 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
Welcome to the Introduction to Microcontrollers course, one of a series of interactive tutorials that introduces and discusses basic facts about microcontrollers (MCUs) and microprocessors (MPUs) and how these semiconductor devices are applied in embedded control systems.
This course explains the differences between MCUs and MPUs, then describes the basic functions built into a microcontroller and lists the main signals used in a typical embedded system. It also lists key questions engineers usually ask when choosing MCUs for new embedded system designs.
Other courses in this series cover the system development cycle; writing code for embedded systems; techniques for debugging application code; MCU datasheets; surface-mount components; the POR, WDT, and LVD (power-on reset, watchdog timer, and low-voltage detection) functions; and on-chip flash memory.

2. 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)
Let’s begin by defining the digital semiconductor devices used in the vast span of applications called embedded systems. Generically, they are called “microcomputers” — or sometimes, “processors.” Basically, microcomputers are physically small computers that perform the specific tasks appropriate to the product or system in which they are used. Examples of such applications include alarm systems, power tools, digital cameras, traffic signals, and a myriad of others.
Acting as the internal “brain” of a product or system, a microcomputer executes functions according a stored set of instructions called application software. The device causes the product or system to act in predetermined and predictable ways, usually in response to various external factors, such as user inputs and signals from external sensors.
From an electronics standpoint, a microcomputer can be described more specifically as a device that contains, at minimum, a central processing unit (CPU), also called a processor core. This fundamental description encompasses two distinctly different device classifications: the microprocessor unit (MPU) and the microcontroller unit (MCU).

3. Differences Between MPUs and MCUs
System implementation
Handheld multimedia phone, car navigation system
Application examples
SH-3 and SH-4 series
Renesas product lines
32 bits or above
Processor 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
MPU
CLASSIFICATION
(Typically, only the CPU Core)
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
CPU Core
I/O
Single chip
The main differences between an MPU and an MCU are historical and functional.
The microprocessor was invented first and is functionally the simplest device. Often it contains just the processor core. For the MPUs used in the latest embedded systems, performance is emphasized. The CPU is a 32-bit or higher design that delivers the high computing power needed to control complex, high-performance products such as handheld multimedia phones and vehicle navigation systems. Such products combine the MPU with external components such as memory chips and peripheral functions.
A microcontroller – sometimes called simply a controller – is a standalone computer. It was invented after the MPU, when semiconductor manufacturing technology eventually made it possible to integrate everything needed for embedded system operation onto a single chip.
Today most MCUs contain a 4-bit to 32-bit processor core and are appropriate for systems that have low to moderate complexity, must be built at low cost, and require a small, compact footprint. MCUs are manufactured in huge volumes — far larger than MPU volumes — and control many, many of the products we use every day, such as washing machines, rice cookers and air conditioners.
Renesas provides both microcontrollers and microprocessors for a wide range of applications. As the bottom row of the table shows, our MPU product lines include the SH-3 and SH-4 series, while our MCU product lines include the M16C, H8, SH-1, and SH-2 series.

4. Typical MCU On-chip Functions
CPU (16-bit H8 type)
Main Clock
Sub-Clock
RAM
ROM
Timer
WDT
ADC
LCD Controller
Serial
Interface
PWM
I/O Port
Example: H8/ bit MCU
Input Port
I/O
Output Port
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
The remainder of this course and the other courses in this series focus on microcontrollers. So now let’s look at a typical MCU in more detail.
To operate in an embedded system, an MCU must at least have a CPU core, memory (RAM and ROM) and one or more clocks. Beyond those basic functions, it may provide many other peripheral functions, the mix of which is usually determined by the application in which the device will be used. Those additional functions may include low-power modes, input/output ports, timers and watchdog timer, pulse width modulator, analog-to-digital converter, serial interface, bus controller, and on-chip debug circuit, among others.
The block diagram shows a Renesas H8-series 16-bit MCU — specifically, a highly integrated H8/38024 device with many useful peripheral functions. As you can see, besides the H8 CPU, RAM, ROM, and clocks, it provides 5 different timers and a watchdog timer, 2 pulse width modulators (PWMs), an analog-to-digital converter (ADC), a serial communication interface, and a liquid crystal display (LCD) controller. All or most of these functions might be used in utility meters, glucose meters, heart-rate monitors and other handheld test instruments, for example.
The pages that follow discuss each of the on-chip functions listed here, in turn, to help you understand the roles they might play in an embedded system built with such an MCU.

5. 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
The processor core is the true brain of an MCU. The CPU fetches software code stored in the on-chip memory and executes the instructions contained in that code. The architecture of the CPU, which includes logic elements, interconnections, and word size, determines the CPU’s code efficiency. In combination with clock speed, it also determines computing performance. For these reasons — among others such as compatibilities within product families — CPU architecture it is the most important characteristic of any MCU or MPU.
There are two basic types of CPU architectures, which basically are defined by their instruction sets. Most MCU CPUs are Complex Instruction Set Computer (CISC) types and have a word size of 4, 8, or 16 bits. (Some have a 32-bit word size.) Most MPUs, however, are Reduced Instruction Set Computer (RISC) types and have word sizes of 32 bits and more. Generally a CISC-type CPU takes more than one cycle to execute an instruction, but has compact code that saves memory space. By contrast, a RISC-type CPU has fewer instructions and executes one instruction per clock cycle for higher performance, but its code takes up more memory space.
One element inside the CPU is the Arithmetic Logic Unit (ALU) that performs calculations that can range from simple arithmetic to complex floating point operations, depending on the sophistication of CPU’s design. Other elements are general registers used for data processing and temporary storage, and specific registers such as the program counter, stack, conditional, and status registers that assist in program control. Also, a series of interconnections called the data bus is used to transport numbers in and out of the processor core. The range of speeds at which the CPU can perform these functions is governed by the frequency of the system clock, which is a function of the voltage supplied to the device.
The computing performance that a CPU can deliver must satisfy the requirements of the intended application. Generally, that performance is measured by comparing some aspect of the computations the CPU can do to a standard benchmark, such as the Dhrystone test. One common standard measurement rating is MIPS, the number of instructions (measured in millions) that the device can execute in one second. A 50MHz RISC MPU with single-cycle execution is a 50-MIPS device, for example. Note, though, that such simplifications and standard benchmark tests give only partial information about device performance and may be misleading at best. How well the MCU or MPU will perform in the actual embedded system is affected by various factors, especially the specific application and the peripherals used.
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

6. Reads & writes, but temporary
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
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 No
Reprogram- mable?
Reads & writes, but temporary
storage only
Now let’s look at an MCU’s on-chip memory, which is used to store the device’s main program and data. There are two types of on-chip memory: Read-Only Memory (ROM) and Random Access Memory (RAM).
ROM is non-volatile memory; that is, it retains the data it stores even when power to the MCU is turned off. For that reason, ROM is used to store application programs, as well as data that remains constant. ROM size on an MCU can be as small as 1KB or as large as 512KB or more.
Various types of ROM can be built into an MCU. Mask ROM contains code that is written into it by making wiring connections during the chip manufacturing process. Programmable ROM (PROM) — also called one-time programmable (OTP) ROM — contains code that is written into it by a programming machine after the chip is manufactured. Once written, the code in mask ROM and PROM/OTP cannot be altered; it can only be read. Flash ROM differs in a fundamental way: The code it contains can be changed (written and read/programmed and reprogrammed) many times. Flash ROM is covered in more detail in another course in this series.
RAM is volatile memory that loses its data when the power to the MCU is turned off. The CPU in the device writes to RAM and reads from it, using it to temporarily store application code and related data while the code is being executed. RAM size can range from 256 bytes to 48KB or more.
The two main types of RAM are dynamic RAM (DRAM) and static RAM (SRAM). DRAM is the most common because it has the smallest memory cell, so more storage can be put into a chip. But to achieve this space efficiency, DRAM requires a periodic refresh process. For this reason among others, DRAM isn’t built into MCUs). Static RAM (SRAM), by contrast, has a larger memory cell but saves power because it holds its contents without refresh for as long as power is supplied. Another type of RAM is cache, which is on-chip memory tightly coupled to the CPUs of high-end processors to maximize performance. The table summarizes facts about data retention and reprogrammability.

7. 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 kHz clock that enables accurate generation of a second frequency via a 16-bit counter
OSC OSC2
MCU
Quartz
crystal C1 C2
Main Clock Circuit
Clocks are essential to MCU operation because they activate and synchronize all states and operations in the device. Typically there are two clock sources: a main clock and a sub-clock.
The main clock drives the CPU and determines its operating speed, and drives other functions as well. The frequency of the main clock, usually measured in megahertz (MHz), can be divided or multiplied, allowing the processor to run at lower or higher speeds. Lower speeds decrease power consumption, while higher speeds increase device performance. The main clock drives various other functions, as well.
Most MCUs have an external main-clock generation circuit that uses a quartz crystal and two capacitors, as illustrated here. However, some MCUs built with advanced semiconductor technology have 40MHz on-chip main clocks that are accurate to ±1% and eliminate the need for the external oscillator circuit components.
The sub-clock generates a second (lower frequency) clock signal that lets the CPU operate at a slower speed to save power in a low-power mode such as Standby mode. It can also be used to drive some of the slower on-chip peripheral functions. The sub-clock typically runs at kHz and enables accurate signal generation via a 16-bit counter.

8. In some of the latest MCUs, Standby mode consumes <1µA
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
The low-power modes enabled by the sub-clock are particularly important for MCUs used in battery-powered portable products because they lengthen the operating time between recharges. But low-power modes are also valuable in many other applications because they reduce energy consumption.
In a typical design, the MCU is driven from the main clock whenever the application requires fast processing. But whenever operation is paused or activities can be performed at a slow pace, the CPU is switched to the lower-speed sub-clock. Low-power modes such as Sleep, Sub-active, and Standby accommodate different system operating needs by providing controls that allow various levels of functionality. To save as much power as possible, for example, unused peripherals are turned off in the Module Stop mode.
Modern MCUs are available that consume miserly levels of power in low-power modes. Some devices built with the latest technology consume less than 1µA in Standby mode.

9. 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.)
In many embedded systems, in order to accomplish its designated tasks the MCU has to communicate with, get data from, and manipulate devices in the “outside world.” The MCU’s general-purpose input and output ports are the essential interfaces used for monitoring and controlling the incoming (input) and outgoing (output) signals used for activities such as communication, external condition monitoring, displaying system status, and driving actuators.
For communication, two main types of input/output (I/O) ports handle bidirectional (two-way) data flows. Parallel I/O ports require a data line for each bit and provide faster data transfer rates. Serial I/O ports transfer bits in sequence using only three signal lines, thus simplifying device packaging and system wiring. Serial I/O ports are the type most often used to access external peripherals.
Input-only ports are typically used to condition the analog signals from physical sensors (temperature, pressure, etc.) that are subsequently converted to digital signals by an on-chip analog-to-digital converter.
Output-only ports can be designed for many purposes. A 20mA, high current I/O port, for example, can directly drive an alarm LED on a display panel. An open collector/drain port, on the other hand, can provide an interface to higher-level supply circuitry or can implement a wired-NOR logic condition.

10. 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
Watchdog Timer
Internal Reset Signal
Overflow
Now let’s examine another important group of functions: timers, which include the watchdog timer (WDT). They control sequences of events or processes in the MCU by counting clock pulses.
A basic timer is a counter that increments (counts up) or decrements (counts down) at a fixed rate related to the pulses of the main system clock or sub-clock. Generally an MCU uses 8-bit or 16-bit timers to measure the timing of events or to generate output signals at the appropriate intervals. A timer might, for example, count down the time during which the MCU performs a certain task. When the timer reaches zero, the task is stopped.
Timers can be used for general-purpose counting or in other modes to perform input capture (IC), output compare (OC), or pulse-width modulation (PWM) functions. Timers often incorporate features designed to satisfy the needs of different applications. In many cases, they can be cascaded together to create larger timing units.
The diagram illustrates a watchdog timer (WDT), which is a special timer often used to implement a safety feature. Basically, the WDT counts upward. If everything in the system is operating correctly, the application periodically resets the WDT before it overflows — a process sometimes called “tickling” or “kicking” the watchdog. But if the software execution becomes erratic or stalls, the application won’t reset the WDT. When the WDT overflows, it triggers a system reset and restart to correct the malfunction.

11. 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
A timer operating in the pulse width modulation (PWM) mode generates a continuous stream of pulses at preset intervals of time. Although the timing of the start of the pulses remains constant, the width of each pulse — and thus the duty cycle — can be set to a value and caused to vary in response to a control signal in the system. Typical waveforms are shown here.
In embedded system applications, the PWM mode is typically used to drive a motor, vary the illumination of an LED, or change the power delivered to other system elements.
PWM Output
Control signal sets nominal width of PWM output pulse and causes it to vary

12. 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
Analog input
Digital output
DAC
(Serial [PWM]
or Parallel)
Analog output
Digital input
Two types of on-chip peripherals link the MCU, which consists mainly of digital circuits, to the real (analog) world: The analog-to-digital converter (ADC or A/D) is an input function. The digital-to-analog converter (DAC or D/A) is an output function.
The ADC receives from signal conditioning circuits analog signals (temperature, pressure, sound, etc.) generated by sensors and transducers. It processes those signals at specific instances of time and converts them into digital data that the MCU can subsequently process. The accuracy and resolution of an ADC are a function of the number of bits in its digital output. Other important ADC characteristics are the converter’s sampling frequency and the conversion technology it uses. The two most common A/D technologies are successive approximation and delta sigma.
The DAC reverses the operation of the ADC, converting digital data into analog form for output. In embedded systems the analog output generally is used to drive actuators or to supply the analog inputs of external user-interface or system-interface devices.
Most MCUs provide an ADC, but far fewer offer a DAC. However, if a DAC function is required, it can be implemented quite easily just by placing an external low-pass filter on a PWM output.

13. 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
Receive message
CAN bus
Prepare
Send message X
CAN #1
CAN #2
CAN #3
CAN #4
CAN: a high-integrity, asynchronous serial data communication bus for automotive and industrial applications
As mentioned previously, the MCU’s serial interface is used to make connections to other parts of the embedded system or to other systems. There are two traditional modes of serial communication: asynchronous and synchronous.
Asynchronous mode is the most widely used. It features data transfer rates, also known as baud rates, of 1200, 2400, and 9600 bits per second.
Synchronous mode is faster because a single clock signal is used in the communication channel to synchronize the data transfer.
An MCU may provide channels for other communication interfaces that transfer data in serial form. Examples include USB, I2C, SPI, LIN, and CAN. Each of these interfaces conforms to a set of industry standards and is optimized for different types of applications and devices. For instance, USB is the most popular interface for connecting peripherals to personal computers. By comparison, the CAN interface highlighted in the illustration is primarily used for connecting systems and subsystems in automotive and industrial applications that mandate highly reliability data transfers in noisy environments.
An asynchronous serial interface generally uses only two pins on the MCU chip: serial in and serial out. A synchronous serial interface generally uses three: serial in, serial out, and clock.

14. 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
External Memory
(DRAM)
Let’s now discuss the bus controller. It’s used in high-performance MCUs in which the CPU has to make accesses to external memory as well as to internal memory. Essentially, as the illustration shows, it acts like a traffic light to ensure that data gets to where and when it is needed.
The address space of the external bus is usually divided into eight areas, and the bus controller manages the bus interface for each of these areas. For example, it determines whether an access to memory is internal or external; standard memory or DRAM. The bus controller also may act as a refresh controller for the DRAM. It manages the length of wait states, provides bus arbitration, and performs other signal-control functions, too, such as those related to direct memory access (DMA) transfers.

15. 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
USB I/F PC
Target Board
OCD Emulator (Example: Renesas E8)
MCU
Typical System Debug Setup
Newly designed MCUs often incorporate on-chip debug (OCD) features that aid system development and debugging. The JTAG interface is commonly used for this purpose. No industry standard yet exists for JTAG debugging, so system engineers usually purchase a debugger or debugging emulator from the MCU manufacturer or implement their own version of the JTAG interface.
The diagram shows the low-cost E8 support product from Renesas, an example of a debugging emulator. It connects to the target system via an interface that can be used both to debug the system and to program the MCU’s on-chip flash memory. The connection to the PC is via a USB port.
Usually just a few pins — mode selection, data in/out, and clock — are required to control the MCU using a “JTAG-like” emulator on a PC. The JTAG debugging signals might be assigned dedicated pins on the MCU or they could be multiplexed with other MCU I/O pins.

16. 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)
Timer A0
ADC
(AN0, AN1)
I/Os
Timer A3
INT3
INT4
INT5
BLDC
INT0
3-phase
Motor
Control
Timer
Hall Sensors
Pulse-width
Measurements
Error
Pulse
OSCD
Currents
DCCT
Pressure Sensor
Bus-voltage
Sensor
(AN2, AN3)
(AN6)
(AN7)
LEDs
IPM
M16C/28
DMA
The previous pages covered the basic functions that an MCU can provide. However, many other peripherals can be built into the device to perform the specific tasks required for particular applications. For example, an embedded system design might require an LCD control function or on-chip circuits for power line communication (PLC), Ethernet media access control (MAC), or 3-phase motor control. Also, it might gain performance advantages from a DMA controller that moves data between functions and memory without CPU intervention. These are but a few of the peripheral-integration possibilities.
To provide additional measures to help ensure that a system will operate safely, extra fail-safe design features beyond the WDT may be incorporated into the MCU. Examples of such functions are low-voltage detection (LVD), power-on reset (POR), and oscillation-stop detection (OSD).
MCU manufacturers offer families of devices with different mixes of on-chip features to help engineers select just the right functionality for maximum cost-effectiveness in diverse embedded system applications. An example of this optimization is the M16C/Tiny motor control application, shown here. The MCU integrates key functions that minimize the need for external components and help keep cost low.
Application example: MCU control of brushless DC motor

17. 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.)
Clock
Mode
Reset
VCC
Debugging (Optional)
Outputs (Control signals, display drive, actuator drives, etc.)
Inputs (keypad, sensors, switches, etc.)
System Requirements
Application Needs
GND
MCU
Interrupts (Internal)
Different types of signals have been mentioned in the previous discussions of MCU functions. They are used to initiate activities and carry information to and from functions within the MCU, in other parts of the embedded system, or in other systems. Generally they can be classified as either system requirements or application needs.
Examples of inputs required by the MCU and the system it implements are power (supply voltage and ground) and external signals such as clock, operating mode, and reset. The MCU uses these signals to start up and maintain proper operation. It also uses interrupts, which are internal signals that adjust system operation when critical events occur. Debugging signals perform a special type of system control required only during system development, so they are an MCU option. All of these signals are described in the hardware manual for the MCU.
Various inputs and outputs are application dependent. Examples of input signals are keypads, sensors, and switches. Examples of application outputs are control signals for motor speed and position, display drives for LCD panels and LEDs, and actuator drives for audio speakers and relays. These signals are defined in the design specifications of the MCU-based product or system being developed.

18. 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
Finally, let’s discuss the factors that engineers consider when they are selecting an MCU for a new development project. Basically, they are looking for a solution that has the MCU that best meets the design specifications for the new product, and also provides the software and hardware tools needed to develop that product in the shortest possible time.
With regard to the MCU, the engineers typically qualify devices by asking the seven questions highlighted in the top oval, among others: • Can the MCU deliver the requisite computing performance? • Are the MCU’s architecture and its compiler good enough to keep code size — and therefore ROM size — to a minimum while executing the application program at a fast speed? • Do the on-chip peripherals meet the needs of the application? • Does the MCU stay within the power budget and meet the product’s “green” environmental requirements? • Does the MCU have good EMC (EMI and EMS) performance that simplifies compliance with the FCC, CE, and related noise standards. • Does the device offer safety features that will help protect the final product when it operates under challenging conditions, or — at minimum — allow it to recover from abnormal operation without causing damage or harming the user? (Most engineers rely on MCU design rather than software implementation to provide this protection.) • Does the MCU use good, reliable flash technology, and can the flash operate fast enough, over the full supply range, and retain data long enough to meet the product’s design requirements?
With regard to support tools, engineers ask the two main questions shown in the bottom oval: • Is the development environment a proven, easy-to-use, and flexible one that offers time-saving features and adequate controls? • Is a complete set of development tools available, including an optimized compiler and affordable hardware tools, especially emulators with sufficient debugging capabilities?
Support tools that shorten system development time
8. Good development environment
9. Complete set of SW/HW tools

19. For more information, please visit our Web site:
Course Summary
Differences between MCUs and MPUs
Functions within an MCU
Basic embedded system signals
Questions engineers ask when choosing an MCU
This concludes the Introduction to Microcontrollers course. You discovered the differences between MCUs and MPUs, then learned the main on-chip functions that a microcontroller provides, and the basic signals of embedded systems. You also saw the questions that engineers typically ask when choosing MCUs for new embedded system designs.
We now invite you to take the other courses in this series, which cover other basic aspects of MCUs and how they are applied. If you want to study material containing greater technical detail, consider taking additional courses at this web site that cover architectures, devices, peripheral functions and more.
Thank you for your interest in Renesas microcontrollers and for taking advantage of the resources of the Renesas Interactive website. Please visit us often. Further, we urge you to bookmark the main Renesas website so you can obtain the latest product, application and support information whenever you need it.
For more information, please visit our Web site: