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Memory, Data Types, And Serial Communication

This very general overview intentionally oversimplifies many complex computer science concepts

Different ways to represent information digitally

Situation: You want to use a light bulb to represent whether zero, one, two, or three students are in a room

- You could use 4 different brightness levels, including full on and full off
  • What about 10 students? 100?
    • It would be hard to tell the difference between that many different light levels

That’s analog. Try digital:

  • Use multiple bulbs and a code
  • Each bulb is either on or off, never in between (binary: one of two values)
  • 4 bulbs let us count up to 15
  • 8 bulbs let us count up to 255
  • 8 bulbs turns out to be a pretty good compromise between the amount of information and the number of bulbs
  • One bulb = 1 binary digit = 1 bit
  • Eight bulbs = 8 bits = 1 byte

Arduino and many other microcontrollers (and early computers) were built around an 8 bit bus (sort of like an 8 lane highway)

  • How would you exchange numbers greater than 256?
  • How would you exchange words?
  • What about non-integers (numbers with fractional parts)?

Examples of ways to represent information with 8 bit:

Memory is just a huge array of bits organized into bytes or multiple bytes

ATmega328: The microcontroller used in the Arduino Uno

  • ATmega328 microcontroller data sheet
  • Block diagram on pg 6
  • AVR diagram on pg 9
  • What are registers? Can be either
    • A generic piece of memory internal to the processor
    • A very specific piece of memory that controls the behavior of some of the hardware
  • What are I/O ports?
    • Pins can be addressed individually (as bits) or in groups of 8 (as bytes)
    • Find the ports in the datasheet (table of contents is at the end) on page 75
    • Integrated Circuit pinout on pg 3

How does Arduino code accomplish what’s in the datasheet?

  • Arduino Uno schematic ( – products – Uno)
  • How does Arduino manipulate the registers, e.g. how does pinMode work? ~/arduino-1.6.8/hardware/arduino/avr/cores/arduino/wiring_digital.c

Serial vs. parallel

  • Parallel modes of transmitting information
    • Moves lots of information quickly
    • Takes lots of wires
  • Alternative?
    • Serial
      • Takes fewer wires
      • requires shifting of data and ways to deal with the timing, which can be done in software or hardware
      • Asynchronous
      • SPI
      • I2C
    • Arduino provides dedicated hardware for these serial interfaces in addition to other dedicated hardware

Related topics :

Shift registers as UARTs Interrupts Timers Binary number system

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