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2. ATmega328P Hardware & Memory Architecture

A. Memory Map

The ATmega328P memory map provides information on how the Microcontroller Unit (MCU) uses memory. Here is the address division:

Category Address Size Description
General Purpose Registers 0x0000 - 0x001F 32 x 8 bit Registers R0 - R31
I/O Registers 0x0020 - 0x005F 64 x 8 bit Accessible via IN/OUT instructions
Extended I/O Registers 0x0060 - 0x00FF 160 x 8 bit Additional I/O registers
Internal SRAM 0x0100 - 0x08FF 2048 x 8 bit Internal data memory

B. General Purpose Working Registers (GPR)

The AVR architecture has 32 general-purpose registers labeled R0 through R31. These registers function as temporary storage for data during processing and are directly connected to the ALU (Arithmetic Logic Unit).

Register Division:

Group Registers Characteristics
Lower Registers R0 - R15 Limited functionality. Cannot store immediate values directly (cannot use LDI instruction).
Upper Registers R16 - R31 More flexible. Can work with immediate data, allowing direct storage of bytes or words.

Pointer Registers:

The last six registers (R26 through R31) can be combined into 16-bit pointers for indirect memory addressing:

Pointer Name Low Register High Register Function
X Register R26 (XL) R27 (XH) Pointer for memory access
Y Register R28 (YL) R29 (YH) Pointer for memory access
Z Register R30 (ZL) R31 (ZH) Pointer for memory & flash access

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