BillHung.Net


powered by FreeFind     sms

Microcontroller Overview Lecture Notes

http://www.media.mit.edu/physics/pedagogy/fab/ucntrl/fabmicronotes.html

What is a Microcontroller?

  • Small, lightweight CPU
  • Some Families:
    • PIC
    • SH1
    • ADuC812
    • 68HC11
  • Allows:
    • Simple hardware to software interface
    • In situ processing (on a PCB, shoe, etc)
    • Less ICs (no more digital logic chips)
  • Has limited:
    • Speed, usually < 5 MIPS
    • RAM, ~ 256 bytes
    • Program storage, 4K instructions
  • Basic Features
    • I/O Pins
      • Usually digital, some analog (see later)
    • Timers
      • 8 or 16 bit
      • Watchdog (resets/wakes up processor after timeout)
    • x Bit operations
      • Usually 8, makes 16 (and greater) bit operations slow
    • External Addressing
      • Gives ability to add extra RAM
  • Hardware UART
    • Allows for serial line communications
    • Can be mimicked in software, but:
      • Slower
      • Uses a timer
      • Cannot trigger interrupt
  • ADC/DAC
    • Analog to Digital / Digital to Analog Conversion
    • Usually 8 bit (up to 16 bits)
    • Usually 20us per sample (down to 5)
    • Can be multiplexed (4051) for more inputs
  • Interrupts
    • Allow asynchronous program flow based on external events
    • Based on:
      • Pin change
      • Serial event
      • Power low (etc)
    • Can wake processor
    • Hard to debug
  • Flash Programmable
    • As opposed to UV erasable (which takes ~15 min)
    • Faster prototyping
    • Sometimes not available with ADC
  • CISC vs. RISC
    • CISC
      • Different instruction sizes and execution times
      • Easier to write assembly language by hand
    • RISC
      • All instructions same size and (almost) same execution time
      • Compiler can usually create smaller code
      • Much easier cycle counting


Some processor families: (Click on name for block diagram)

  • PIC  (www.microchip.com)
    • Usually:
      • 18 - 28 pin packages (down to 8) with 14-22 I/O
      • ADC available, usually 4 channels, 8 bits
      • Max. 5 MIPS
    • Hardware UART on heavier chips
    • No external addressing
    • Excellent general purpose chips
    • Ubiquitous around the Lab
  • SH1 7032 (eg of Hitachi SH family) (semiconductor.hitachi.com/superh/)
    • Lots of:
      • Speed (20 MIPS)
      • Bits (32)
      • RAM (8K)
      • 16 bit timers (5)
      • Interrupts (40)
      • Power drain (100 mA)
      • Pins to solder (100)
         
  • ADuC812 (www.analog.com/industry/microconverter)
    • Fast (5 us) 8 channel, 12 bit ADC
    • Hardware UART
    • Flash
    • But:
      • CISC
      • 1.25 MIPS max
    • Still good for data collection, smart sensor type application
Edited 11/05/99 by Ari Benbasat