Microcontroller Components

• Central Processing Unit (CPU)
  • Contains arithmetic circuits, the called Arithmetic Logic Unit (ALU)
  • Executes instructions
• Memory
  • Holds the program(s)
  • Holds data program(s) operate on
• Input Port(s)
  • Allows info to enter from the outside world
  • PORTA¹⁾
  • PORTB
  • PORTC
  • PORTD²⁾
• Output Port(s)
  • Allows info to be sent to the outside world
  • PORTA³⁾
  • PORTB
  • PORTC
  • PORTD⁴⁾
• All ports are 8-bits wide

Memory Types

There are two types of memory:

• Read/Write
  • typically this memory is volatile — must keep power applied to memory chip in order for it to keep its state
  • Two types:
    • Static Random Access Memory (SRAM) — found on the ATmega32
      • Uses a flip-flop to store state
    • Dynamic Random Access Memory (DRAM) — found on
      • Uses capacitor to store state
      • Must refresh memory state frequently or capacitor will lose its charge
      • Can get in high density
• Read Only Memory (ROM)
  • typically this memory is non-volatile — keeps its state even without power
  • FLASH
  • EEPROM — Electrically Erasable Programable Read Only Memory
    • Actually can write to it, but writing is very slow compared to reading

The ATmega32 uses SRAM for data and FLASH memory for the program

• This is know as the Harvard Architecture which is used by many modern processors
• This means that your program will still be there the next time you turn your board on, it will run your program (but all data will be lost)
• The Harvard architecture is safer because it prevents the program from overwriting itself and then executing the data

SRAM

• Allows storage of 1's and 0's
• The data is stored in groups of 8 bits per location
• Memory is organized as an array
• Each location has a unique address
• The ATmega32 has 2KiB (2048 bytes)
• We could represent each unique address with 11 bits, but the ATmega32 uses 16 bit address
• 0x60 is the first available address of SRAM
• 0x85F is the the last available address of SRAM

FLASH

• Also stores 1's and 0's
• The data is stored in groups of 16 bits per location
• Memory is organized as an array
• Each location has a unique address
• The ATmega32 has 32KiB (32768 bytes)
  • Often 32KiB is referred to as 32KB, but as of November 2000, the correct prefixes for binary multiples are kibibytes (KiB), mebibytes (MiB), gibibytes (GiB), etc.
• Since each location is 16 bits, we have 32768/2 = 16384 locations
• We would need 14 bits to represent each unique address, since 2¹⁴ = 16384

Programmable Registers

• ATmega32 has 32 registers
• The registers are each 8 bits wide
• They are located at r0 through r31
• The registers are located in SRAM at addresses 0x00 through 0x1F