Lecture 7: Microcontroller Architecture

1
Lecture 7 Microcontroller Architecture

• Lecturer
• Mr Robert Ross

2
Overview

• Transistor Gate model
• Equivalent Gate Circuits
• MSP430 Microcontroller Architecture

3
Microprocessor Elements

• Microprocessors are not magic
• They are collections of logic gates which are
  controlled by instructions stored in memory
• Memory is a collection of logic gates
• Logic gates are made up of transistors
• Microprocessors are essentially large,
  reconfigurable state machines

4
Digital Transistor Model

• The control line (Base) is used to open/close
  switch
• If voltage applied then switch closes, otherwise
  is open
• Switch decides state of transistor
• Open no current flowing through (0 state)
• Closed current flowing through (1 state)

In (Collector)
Control (Base)
Out (Emitter)
5
Transistor Model - AND Gate
Power Supply
Input 1
Input 2
Output
6
Transistor Model - OR Gate
Power Supply
Input 1
Input 2
Output
7
Transistor Model - NOT Gate
Power Supply
Output
Input 1
8
AND Gate Equivalent

• AND Gates can be constructed using NAND Gates and
  an Inverters

9
OR Gate Equivalent

• OR Gates can be constructed using NAND Gates and
  an Inverters

10
NOT Gate Equivalent

• NOT Gates (inverters) can be constructed using
  NAND Gates

11
Hardware Summary

• All gates can be expressed as combinations of
  NAND gates
• Microprocessors can implement all logic functions
  using NAND gates made up from discrete transistors

12
Intro to MSP430 Microcontroller

• MSP430F2013 Microcontroller
• Key Features
• Low power (0.1uA Power Down, 0.8uA Standby) (10
  years off a lithium battery)
• 16 Bit RISC processor
• Universal serial interface
• 2kB Flash, 128B RAM
• 16 Bit Sigma-Delta ADC
• Embedded emulation

13
MSP430 Microcontroller Architecture
14
MSP430 - CPU

• 16-Bit RISC Processor
• 16 Registers (16 Bit)
• von Neumann Architecture
• 51 Assembly Instructions
• 27 Core
• 24 Emulated
• 7 Addressing modes

15
MSP430 Clock System

• Flexible 3 different clocking sources
• Low Frequency Crystal Clock (LFXTCLK) External
  low frequency clock 32kHz watch crystal
• Crystal 2 Clock (XT2CLK) External high speed
  clock - 400kHz to 16MHz
• Digitally Controlled Oscillator Clock (DCOCLK)
  Internally generated clock. Default clock source
  for the master clock upon reset. Default
  frequency 900kHZ (can be slowed down)
• Three clock lines different clocks can be used
  by different parts of the system
• Lower clock speed minimises power consumption

16
MSP430 Spy-Bi Wire

• TI Proprietary two wire protocol
• Lower pin count than JTAG (4 pins)
• The computers interface to the microprocessor

17
MSP430 - JTAG

• Joint Test Action Group (IEEE 1149.1)
• Mechanism by which the computer communicates with
  the microprocessor and memory
• Computer interfaces with JTAG via Spy-Bi Wire
• Emulator connected to JTAG to allow PC
  communications

18
MSP430 Flash (ROM)

• 2KB Flash
• Bit, byte or word programmable
• Can be programmed via JTAG
• This is where code is programmed into
• FCTL1, FCTL2 and FCTL3 are registers to control
  the flash

19
MSP430 - RAM

• 128 Bytes of RAM
• Start address 200h
• Stack Stored in RAM (grows backwards from 0x0280)

20
MSP430 Memory Map

• Family memory map
• For the MSP430F2013
• RAM 0x00200 0x0027F
• Flash 0xF800 0xFFFF

21
MSP430 A/D Converter

• 16 Bit Sigma Delta ADC
• 8 input channels
• Built in temperature sensor
• Selectable external or internal (1.2V) reference

22
MSP430 Ports P1P2

• P1 has 8 GPIO Pins
• P2 has 2 GPIO Pins
• All 10 pins are capable of driving interrupts
• One interrupt vector per port
• Internal, selectable pull-up/down resistors

23
MSP430 Watchdog Timer

• In case of a software fault the WDT performs a
  controlled system restart
• If the selected WDT expires (without being reset
  in software) restart will be initiated

24
MSP430 Timer_A2

• 16 bit timer
• Two capture compare registers
• Used to generate interrupts
• Supports
• PWM Generation
• Interval timing
• Modes
• Up Repeatedly counts from 0 to TAACR0
• Continuous Repeatedly counts from 0 to FFFF
• Up/Down Repeatedly counts from 0 to TACCR0 then
  back to 0

25
MSP430 - USI

• Universal Serial Interface
• Three-wire SPI mode support
• I2C mode support
• Selectable Endianness
• Contains shift register, bit counter and logic to
  facilitate SPI or I2C
• Programmable clock generation

26
MSP430 - Emulator

• Full speed, real time emulation
• Supports breakpoints, single steps and complex
  triggering
• In-system development (not software model)
• No application resources required

27
MSP430 Brownout Detection

• Detects if supply voltage has dropped and
  performs reset.
• Cleans up mechanically induced voltage
  fluctuations (eg. battery insertion)

28
Summary

• Transistors are the basic building block for
  microprocessors
• The MSP430 is a microcontroller which includes a
  CPU, memory and other peripherals like an ADC
• Next lecture will investigate the architecture of
  the MSP430 CPU