Atmel ATtiny25 User Manual

75
7598H–AVR–07/09
ATtiny25/45/85
Notes: 1. MAX = 0xFF
2. BOTTOM = 0x00
12.8.2 Timer/Counter Control Register B – TCCR0B
• Bit 7 – FOC0A: Force Output Compare A
The FOC0A bit is only active when the WGM bits specify a non-PWM mode.
However, for ensuring compatibility with future devices, this bit must be set to zero when
TCCR0B is written when operating in PWM mode. When writing a logical one to the FOC0A bit,
an immediate Compare Match is forced on the Waveform Generation unit. The OC0A output is
changed according to its COM0A1:0 bits setting. Note that the FOC0A bit is implemented as a
strobe. Therefore it is the value present in the COM0A1:0 bits that determines the effect of the
forced compare.
A FOC0A strobe will not generate any interrupt, nor will it clear the timer in CTC mode using
OCR0A as TOP.
The FOC0A bit is always read as zero.
• Bit 6 – FOC0B: Force Output Compare B
The FOC0B bit is only active when the WGM bits specify a non-PWM mode.
However, for ensuring compatibility with future devices, this bit must be set to zero when
TCCR0B is written when operating in PWM mode. When writing a logical one to the FOC0B bit,
an immediate Compare Match is forced on the Waveform Generation unit. The OC0B output is
changed according to its COM0B1:0 bits setting. Note that the FOC0B bit is implemented as a
strobe. Therefore it is the value present in the COM0B1:0 bits that determines the effect of the
forced compare.
Table 12-7. Waveform Generation Mode Bit Description
Mode WGM2 WGM1 WGM0
Timer/Counter
Mode of
Operation TOP
Update of
OCRx at
TOV Flag
Set on
(1)(2)
0 0 0 0 Normal 0xFF Immediate MAX
10 0 1
PWM, Phase
Correct
0xFF TOP BOTTOM
2 0 1 0 CTC OCRA Immediate MAX
3 0 1 1 Fast PWM 0xFF TOP MAX
4 1 0 0 Reserved – – –
51 0 1
PWM, Phase
Correct
OCRA TOP BOTTOM
6 1 1 0 Reserved – – –
7 1 1 1 Fast PWM OCRA TOP TOP
Bit 7 6 5 4 3 2 1 0
FOC0A FOC0B – – WGM02 CS02 CS01 CS00 TCCR0B
Read/Write W W R R R/W R/W R/W R/W
Initial Value 0 0 0 0 0 0 0 0

Atmel ATtiny25 Specifications

General

Architecture	AVR
Flash Memory	2 KB
SRAM	128 B
EEPROM	128 B
Clock Speed	20 MHz
I/O Pins	6
PWM Channels	2
Operating Voltage	1.8V - 5.5V
ADC	4 channels, 10-bit
Communication Interfaces	SPI, I2C, USART
Operating Temperature Range	-40°C to 85°C
Timers	8-bit Timer/Counter with PWM, 16-bit Timer/Counter with PWM
Package	8-pin PDIP, SOIC-8

Summary

Features

Overview and Pin Configurations

Pinout

Pin configuration details for ATtiny25/45/85, showing pin functions for SOIC and QFN packages.

Overview

Introduces the ATtiny25/45/85 as a low-power AVR microcontroller with RISC architecture.

AVR CPU Core

Architecture & Registers

Covers CPU core, architectural overview, ALU, status, and general purpose registers.

Instruction Execution & Reset/Interrupts

Details instruction timing, reset, and interrupt handling mechanisms.

ATtiny25/45/85 Memories

Flash, SRAM, EEPROM, and I/O Memory

Describes Flash, SRAM, EEPROM, and I/O memory spaces and their characteristics.

System Clock and Clock Options

Clock Sources and Prescalers

Details clock sources (RC, Crystal, PLL) and the system clock prescaler.

Power Management and Sleep Modes

MCU Control Register

Details the MCU Control Register for power management and sleep mode selection.

Sleep Modes (Idle, ADC Noise Reduction, Power-down)

Explains the different sleep modes and their features for power saving.

Power Reduction Register

Describes the PRR for stopping clocks to peripherals to reduce power consumption.

System Control and Reset

Reset Sources

Lists and describes the various reset sources like Power-on, External, Watchdog, and Brown-out.

Brown-out Detection

Details the On-chip Brown-out Detection (BOD) circuit and its configuration.

Interrupts

Interrupt Vectors in ATtiny25/45/85

Lists the interrupt vectors and their definitions for ATtiny25/45/85.

I/O Ports

Ports as General Digital I/O

Covers port configuration, general I/O, and switching between input/output.

Alternate Port Functions

Explains alternate functions of port pins and overriding signals.

Register Description for I/O-Ports

Details the PORTB, DDRB, and PINB registers for I/O port control.

External Interrupts

MCU Control Register – MCUCR

Details the External Interrupt Control Register for interrupt sense control.

General Interrupt Mask Register – GIMSK

Covers the GIMSK for enabling external and pin change interrupts.

8-bit Timer/Counter0 with PWM

Modes of Operation and Registers

Explains operational modes and register descriptions for Timer/Counter0.

Counter and Compare Units

Timer/Counter1 and Dead Time Generator

Details Timer/Counter1 operation and the Dead Time Generator for PWM.

Universal Serial Interface – USI

Functional Descriptions and Registers

Covers USI modes (3-wire, SPI, 2-wire) and register descriptions.

Analog Comparator

ACSR and ADCSRB Registers

Details Analog Comparator Control and Status Registers for configuration and interrupts.

Analog Comparator Multiplexed Input

Explains selecting ADC pins as the negative input to the Analog Comparator.

Analog to Digital Converter

ADC Features and Operation

Lists ADC features and describes its operation, including channel and reference selection.

Starting a Conversion

Explains manual and auto-triggered ADC conversion start methods.

ADC Conversion Result

Details how to read and interpret ADC conversion results in different modes.

debugWIRE On-chip Debug System

Features, Interface, and Registers

Covers debugwire features, physical interface, limitations, and registers.

Memory Programming

Lock Bits and Fuse Bytes

Explains memory lock bits and the functionality of fuse bytes.

Serial Downloading

Details serial programming methods including SPI and HVSP.

High-voltage Serial Programming

Covers programming Flash, EEPROM, Lock bits, and Fuse bits using HVSP.

Electrical Characteristics

Absolute Maximum Ratings*

Lists the stress ratings that may cause permanent damage to the device.

DC Characteristics

Provides DC characteristics across temperature and voltage ranges.

Typical Characteristics

Supply Current (Active, Idle, Power-down)

Shows supply current graphs for different modes versus frequency and VCC.

Pin Characteristics (Pull-up, Driver Strength, Thresholds)

Details pin pull-up, driver strength, and threshold characteristics.

Oscillator and BOD Characteristics

Covers BOD thresholds and internal oscillator frequency characteristics.

Register Summary

Instruction Set Summary

Ordering Information

Package Types

Lists available package types like T5 and PC with their specifications.

Document Revision History

Errata