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

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

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

¹⁾ , ³⁾ Also contains A/D converter

²⁾ , ⁴⁾ PORTD0 and PORTD1 are used for serial communication on the SunRom boards