Microcontrollers : Applications and Architectures

1
Microcontrollers Applications and
Architectures   
EE1A2 

• Sandra I. Woolley
• Electronic, Electrical and Computer Engineering

2
Introductory Assembler Exercises

• Let us look at some examples of PIC16F84
  microcontroller assembler instructions. What do
  these instructions do?
• At the start, the working register (W) contains
  the value 0x1C and the PORTB register contains
  the value 0. What values are in W and PORTB
  after each instruction?
• MOVLW 0X24
• ADDLW 0X02
• ADDLW 0X17
• MOVWF PORTB
• CLRW
• ADDLW 0x05
• MOVWF PORTB
• CLRF PORTB

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Contents

• Microcontrollers and Embedded Systems
• Applications
• Architectures
• Von Neuman and Harvard
• CISC vs. RISC
• PIC16F84 Memory
• Assembler Instruction Exercises

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Introduction

• A microprocessor is a programmable logic device
  with a designed set of instructions. It contains
  three primary components a processing unit,
  memory, and, input and output (I/O).
•  
• A controller is used to control some process or
  aspect of the environment.
• At one time, controllers were built exclusively
  from logic components, and were usually large,
  heavy boxes.
• With the advent of microprocessors entire
  controllers could fit on a small circuit board.
• You can still find controllers powered by one of
  the many common microprocessors (e.g., Zilog
  Z80).
• But most new systems use microcontrollers
  robust, low-power, single-chip solutions designed
  specifically for the embedded control
  environment.
•  

5
Embedded Systems

• Embedded system definition from Wikipedia, the
  free encyclopedia.
• An embedded system is a special-purpose computer
  system, which is completely encapsulated by the
  device it controls.
• An embedded system has specific requirements and
  performs pre-defined tasks, unlike a
  general-purpose personal computer.
•  

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Example Applications of Embedded Microcontrollers

• Households appliances
•    microwave ovens
•    refrigerators
•    televisions and VCRs
•    stereos
• Computers and computer equipment
•    laser printers
•    modems
•    disk drives
• Cars
•    engine control
•    diagnostics
• Environmental control
•    greenhouse, factory, home
•  

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More on Applications

• Small size and low power consumption also make
  microcontroller devices ideal for unattended data
  monitoring and recording.
• The automotive market an important driving force
  in the microcontroller market, especially at its
  high end. The systems must operate under extreme
  temperatures and be able to withstand vibration,
  shock, and EMI.
•  

Embedded Car Area Network (CAN) Devices
8
Smart Card Applications
www.wincoid.com/ ph_smart.htm
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Von Neuman and Harvard Architecture

•  
• Von Neuman Architecture
• Program instructions and data are stored in a
  common main memory.
• Microcontrollers based on the Von-Neuman
  architecture have a single bus that is used to
  fetch both instructions and data.
• Harvard Architecture
• Microcontrollers based on the Harvard
  Architecture have separate data and instruction
  memories.
•  
•  

10
CISC vs. RISC

• CISC (Complex Instruction Set Computer)
• Many modern microcontrollers are based on the
  CISC concept.
• The typical CISC microcontroller has well over 80
  instructions, many very powerful and specialised.
  
• It is quite common for the instructions to all
  behave quite differently.
• The advantages of the CISC architecture is that
  many of the instructions are macro-like,
  allowing the programmer to use one instruction in
  place of many.
•  
• RISC (Reduced Instruction Set Computer)
• The benefits of RISC design simplicity are a
  smaller chip, smaller pin count, and very low
  power consumption.

11
PIC16F84 Memory

•  
• There are two memory blocks in the PIC16C84
• program memory and data memory.
• Each block has its own bus, so that access to
  each can occur during the same clock cycle.
•  
• The data memory can be further broken down into
  general purpose memory and special purpose
  registers 

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PIC16F84 Program Memory
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PIC16F84 Data Memory
(This is a simplified memory map that excludes
bank1. Study the memory banks in the Microchip
data sheets).
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PIC16F84 Register-Mapped I/O
When ports are configured as outputs, bits sent
to the PORTA and PORTB registers are
automatically output. When configured as inputs,
any received inputs affect the values of the
corresponding register contents.   PORTA is 5
bits wide and PORTB is 8 bits wide. Each port
can be programmed as an input or an output.
(Bit 4 of port A can be used for an external
timer input.)   PORTA has pins/bits labelled
RA4RA0 and PORTB has pins/bits labelled RB7RB0
Referencing bits . Bits are numbered 7-0 from
left to right, i.e., msb-lsb. One of the most
common programming errors is incorrect
specification of bit numbers.    
15
Using I/O Ports

• WRITTEN BY SIW
• DATE 01/01/2004
• FILE SAVED AS TEST.ASM
• DEVICE 16F84
• OSCILLATOR XT (4MHZ)
• WATCHDOG DISABLED
• FUNCTION OUTPUTS THE VALUE 0XF1 TO
  8 LEDS CONNECTED TO PORTB
• ----------------------- EQUATES
  ------------------------------------
• PORTB EQU 0X06 ASSIGN THE PORTB
  REGISTER TO THE LABEL 'PORTB'
• ----------------------- MAIN PROGRAM
  ------------------------------------
• START ORG 0X00 'ORG' SPECIFIES THE
  MEMORY LOCATION OF THE PROGRAM
• MOVLW 0X00 MOVE THE VALUE 00, I.E.,
  ALL 0'S TO W
• TRIS PORTB CONFIGURE PORTB WITH THE
  VALUE IN W (THE
• WORKING REGISTER)
  1INPUT AND 0OUTPUT.
• SO 00 (ALL 0'S) MAKES
  ALL PORTB LINES OUTPUTS.
• CLRF PORTB CLEAR THE PORTB REGISTER
• MOVLW 0XF1 MOVE THE HEX VALUE F1 TO
  THE WORKING REGISTER
• MOVWF PORTB OUTPUT THE VALUE TO
  PORTB
• LOOP GOTO LOOP

16
Assembler Code Exercises

• What do these instructions do?
• At the start, the working register (W) contains
  the value 5 and the PORTB register contains the
  value 0. What values are in W and PORTB after
  each instruction?
• MOVLW 0X13
• ADDLW 0X28
• MOVWF PORTB
• INCF PORTB,1
• INCF PORTB,0
• BCF PORTB,2
• 2. The following equates assign the label F to
  1 and W to 0. Why is this useful?
• F EQU 1
• W EQU 0
• So we can write INCF PORTB,F instead of INCF
  PORTB,1
• 3. Why is there no END instruction in the list
  of PIC instructions?
• Why does our example program end with LOOP
  GOTO LOOP