CPU configuration and definitions for ATmega168. More...

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Macros
#define	__AVR_ATmega168__
	ATmega168 microcontroller selection.

#define	BAUD 9600UL
	Default USART baud rate for serial communication.

#define	F_CPU 16000000UL
	CPU clock frequency in Hertz.

Detailed Description

CPU configuration and definitions for ATmega168.

Author: Roybel Carbonell Camejo

Date: 2026-04-29

Version: 1.0

This header file centralizes all CPU-specific configurations for the ATmega168 microcontroller. It defines the processor type, clock frequency, and default serial communication baud rate.

Usage

Include this file before any AVR-specific headers or other modules that depend on CPU definitions:

#include "includes/CPU.h"
#include <avr/io.h>
#include <util/delay.h>

Dependencies

No external dependencies required

Notes

This file should be included BEFORE <avr/io.h> to ensure proper CPU definition
F_CPU is required by <util/delay.h> for accurate delay calculations
BAUD is used by USART modules for serial communication configuration

Warning: If F_CPU is not defined correctly, timing functions like _delay_ms() will produce incorrect delays.; Changing BAUD requires matching configuration on the serial terminal side.

Definition in file CPU.h.

Macro Definition Documentation

◆ __AVR_ATmega168__

#define __AVR_ATmega168__

ATmega168 microcontroller selection.

Ensures the compiler uses the correct memory map, register definitions, and hardware-specific optimizations for the ATmega168.

This macro is:

Required by avr-libc headers
Used by avr-gcc for proper code generation
Essential for correct interrupt vector table mapping

Note: The conditional guard prevents redefinition if already set by compiler flags

See also: https://www.nongnu.org/avr-libc/user-manual/using_tools.html

Definition at line 52 of file CPU.h.

◆ BAUD

#define BAUD 9600UL

Default USART baud rate for serial communication.

Sets the serial communication speed to 9600 bits per second. This is a standard baud rate commonly used for microcontroller communication and terminal interfaces.

Range of typical baud rates for ATmega168 @ 16MHz:

2400, 4800, 9600, 14400, 19200, 28800, 38400, 57600, 115200

Note: The actual achievable baud rate depends on F_CPU and UBRR register precision

Warning: Baud rate error should ideally be less than 2% for reliable communication

Calculation formula:

UBRR = (F_CPU / (16 * BAUD)) - 1
For F_CPU=16MHz, BAUD=9600: UBRR = (16000000 / (16 * 9600)) - 1 = 103.166 → 103
Error = 0.16% (well within acceptable range)

See also: F_CPU Required for baud rate calculation; USART.h Where this BAUD definition is typically used

Examples: /home/luka/WORK/Programming/ARDUINO/AVR-Square-Wave-Organ/src/includes/CPU.h.

Definition at line 79 of file CPU.h.

◆ F_CPU

#define F_CPU 16000000UL

CPU clock frequency in Hertz.

Defines the operating frequency of the ATmega168 microcontroller as 16 MHz. This macro is critical for timing functions and peripheral configuration.

Important uses:

Used by <util/delay.h> for _delay_ms() and _delay_us() functions
Required for USART baud rate calculations
Used in timer/Counter configurations
Affects PWM frequency calculations
Used for SPI and I2C timing

For ATmega168 typical clock configurations:

1 MHz (default internal RC oscillator)
8 MHz (internal RC oscillator calibrated)
16 MHz (external crystal, as used here)
20 MHz (maximum recommended with external crystal)

Note: This value MUST match the actual hardware clock configuration

Warning

If F_CPU is incorrect:

_delay_ms() will be too fast or too slow
USART will have baud rate errors
Timer-based code will fail

Derivation for UBRR calculation:

UBRR = (F_CPU / (16 * BAUD)) - 1
     = (16000000 / (16 * 9600)) - 1
     = (16000000 / 153600) - 1
     = 104.166 - 1
     = 103.166 → 103 (integer)

See also: BAUD Used together with F_CPU for baud rate calculation; sleep.h Used for sleep mode timing

Examples: /home/luka/WORK/Programming/ARDUINO/AVR-Square-Wave-Organ/src/includes/CPU.h.

Definition at line 121 of file CPU.h.

Macros