Embedded Systems: Atmega328P Microcontroller

Atmel ATmega328P Microcontroller

• 8-bit Atmel ATmega328/P microcontroller used in ARDUINO UNO R3 Board
• Introduced in 1996, adopts a modified Harvard architecture
• Program and data stored in separate physical memory address spaces, but can read data from program memory using special instructions

AVR CPU

• AVR family of microcontrollers divided into four subgroups: Tiny AVR, Mega AVR, XMega AVR, and Application-specific AVR
• AVR CPU based on Reduced Instruction Set Computing (RISC) architecture
• Single cycle execution, 32 general purpose registers

ATmega328P Features

• Low-power CMOS 8-bit microcontroller
• 28/32 pins
• CMOS: Complementary Metal-Oxide-Semiconductor
• RISC (Reduced Instruction Set Computing) architecture

Endianness

• Little-endian: least significant byte of data is placed at byte with lowest address
• Big-endian: most significant byte of data is placed at byte with lowest address

Packages

• Different ATMega328 packages: Micro Leadframe or Quad-flat no-leads (MLF/VQFN), Quad-flat Package (TQFP), Dual in-line Package (DIP)

Pin Descriptions

• Pin descriptions available on Atmel ATmega328/P pages 17-20

AVR CPU Core

• ALU (Arithmetic Logic Unit) performs arithmetic operations between registers or between a register and an immediate
• 32 general purpose registers (R0-R31) directly connected to ALU
• 8-bit Status Register (SREG) stores information about the result of the most recently executed arithmetic instruction
• Program Counter (PC) and Instruction Register
• Instruction Decoder and Stack Pointer (SP)

ALU Operations

• Divided into three main categories: Arithmetic, Logical, and Bit-functions
• Some implementations of ALU provide a powerful multiplier supporting both signed/unsigned multiplication and fractional format

AVR CPU Registers

• 32 general-purpose registers with single clock cycle access time
• Six of the 32 registers can form 16-bit address pointers (X, Y, and Z pointers) for addressing data memory
• Z register can also be used as an address pointer to read from and/or write to the flash program memory, signature rows, fuses, and lock bits

Status Register (SREG)

• Contains information about the result of the most recently executed arithmetic instruction
• Bit 7 (I): Global Interrupt Enable, must be set to 1 to enable interrupts, cleared to 0 to disable interrupts

AVR Stack Pointer (SP)

• Address of the Stack area where the interrupts and subroutine Stacks are located
• SP points to the data SRAM Stack area
• The Stack grows from higher to lower memory locations
• SP is implemented as two 8-bit registers

Test your knowledge about the Atmel ATmega328P microcontroller, including its CPU, instructions, memory model, addressing modes, and relation to Arduino UNO R3 board. This quiz aligns with CLO 2 of the Introduction to Embedded Systems course by Dr.Abdulmalik Alwarafy for Spring 2024.