registers to be accessed in one single instruction executed in one clock cycle. The resulting
architecture is more code efficient while achieving throughputs up to ten times faster than con-
ventional CISC microcontrollers.
The ATtiny25/45/85 provides the following features: 2/4/8K byte of In-System Programmable
Flash, 128/256/512 bytes EEPROM, 128/256/256 bytes SRAM, 6 general purpose I/O lines, 32
general purpose working registers, one 8-bit Timer/Counter with compare modes, one 8-bit high
speed Timer/Counter, Universal Serial Interface, Internal and External Interrupts, a 4-channel,
10-bit ADC, a programmable Watchdog Timer with internal Oscillator, and three software select-
able power saving modes. The Idle mode stops the CPU while allowing the SRAM,
Timer/Counter, ADC, Analog Comparator, and Interrupt system to continue functioning. The
Power-down mode saves the register contents, disabling all chip functions until the next Inter-
rupt or Hardware Reset. The ADC Noise Reduction mode stops the CPU and all I/O modules
except ADC, to minimize switching noise during ADC conversions.
The device is manufactured using Atmel’s high density non-volatile memory technology. The
On-chip ISP Flash allows the Program memory to be re-programmed In-System through an SPI
serial interface, by a conventional non-volatile memory programmer or by an On-chip boot code
running on the AVR core.
The ATtiny25/45/85 AVR is supported with a full suite of program and system development tools
including: C Compilers, Macro Assemblers, Program Debugger/Simulators, In-Circuit Emulators,
and Evaluation kits.
2.2 Pin Descriptions
2.2.1 VCC
Supply voltage.
2.2.2 GND
Ground.
2.2.3
Port B (PB5..PB0)
Port B is a 6-bit bi-directional I/O port with internal pull-up resistors (selected for each bit). The
Port B output buffers have symmetrical drive characteristics with both high sink and source
capability. As inputs, Port B pins that are externally pulled low will source current if the pull-up
resistors are activated. The Port B pins are tri-stated when a reset condition becomes active,
even if the clock is not running.
Port B also serves the functions of various special features of the ATtiny25/45/85 as listed on
page 60.
On the ATtiny25 device the programmable I/O ports PB3 and PB4 (pins 2 and 3) are exchanged
in the ATtiny15 compatibility mode for supporting the backward compatibility with ATtiny15.
2.2.4 RESET
Reset input. A low level on this pin for longer than the minimum pulse length will generate a
reset, even if the clock is not running. The minimum pulse length is given in Table 8-1 on page
37. Shorter pulses are not guaranteed to generate a reset.
4 ATtiny25/45/85
2586AS–AVR–02/05