Ethernut 3



ARM microcontrollers have developed to become undisputed market leaders. Ethernut 3.1 is a network compatible single board computer based on the ARM7TDMI, which is combined with a programmable logic module.

The third generation of the Ethernut family offers quick response time with minimal power consumption. Running in internal RAM the 32-bit CPU processes around 72 million commands per second and the programmable logic enables the implementation of special hardware interfaces. 8 MByte´s of flash storage and a socket for MMC/SD cards offer sufficient capacity for more challenging tasks.

Like all other Ethernut boards, it provides an extension connector for attaching additional hardware. Hence it is suitable for both the prototyping of your own hardware as well as for direct integration into your finished product.

Ethernut boards come in use where robustness, reliabilty and long-term availability play a vital role. Our in-house quality control procedures guarantee a consistently high level of reliability.

The main characteristics of Ethernut 3.1 boards are:

  • Fast 32-bit RISC CPU with 256 kByte RAM for CPU-intensive calculations and fast responses
  • Programmable logic with 3,200 gates to implement special hardware
  • 8 MByte Flash memory for programs and web server content
  • 4 MByte non-volatile serial data memory
  • Memory mapped Ethernet controller with 100BASE-T connector and Auto-MDIX support
  • RS-232 connector to control and monitor external devices
  • 14 digital 3.3 V I/O ports, additionally offers counter I/O and USART
  • 24 digital I/O ports as external memory bus or programmable 3.3 V logic, 5 V tolerant
  • Multimedia/SD card slot to easily exchange data
  • JTAG connector for programming and debugging
  • Single 5-24 V power supply


Application development is carried out in the high level programming language C, using either free GNU tools or the commercially supported ImageCraft compiler.

An active Open Source community developed and managed Nut/OS, a cooperative multithreading operating system with TCP/IP stack, which was specially designed with tiny embedded systems in mind. The well documented source code provides a convenient user interface, which is very similar to the C programming of desktop PC’s. Programmers will therefore quickly feel at ease operating this.

Although pre-configured for Ethernut 3.1, all important settings can be customized with just a few mouse clicks with an easy to use graphical interface available on Linux, Windows and Mac OS X PCs incorporating any special requirements. A complete Internet enabled web server needs about 100 kByte Flash and 20 kByte RAM. This leaves enough space for ambitious product ideas, including a boot loader for the update of firmware via the network. Many useful example applications are included in the distribution.


The entire source code for the target system, as well as the hardware design, have a permissive BSD Licence. This is available for commercial products without any licence fees.

In contrast to some other Open Source licence models, there is no obligation to publish your own source code enhancements.


CPU AT91R40008, 73.728 MHz Clock
Flash memory External 4 MByte
Static RAM Internal 256 kByte
Serial Flash External 4 MByte
RTC Hardware (PCF8563T)
Ethernet RJ-45 10/100Base-T (DM9000A)
RS-232 1 x 9-pin DcE 8-Wire, 1 x TTL/CMOS
Digital I/O 17 configurable GPIO lines with alternate functions
Analog I/O None available
Programming 10-pin JTAG
Indicators Power (red), link (yellow), activity (green), user (green)
Power supply
Regulator 600 mA switcher (LT1616)
Input 2.1 mm barrel connector, unregulated 7 to 24 V DC
Expansion Port 5 to 24 V unregulated or 3.3 V regulated, output > 1 W
Consumption < 1.2 W at 12 V
Battery Backup Double layer cap for realtime clock
RS-232 15 kV ESD protection
Ethernet Transformer isolation
Power supply 1 A replaceable fuse, rectifier bridge, current limiter, thermal shutdown
Operating temperature 0 to 70 °C (32 to 158 °F)
Storage temperature -65 to 140 °C (-85 to 284 °F)
Humidity 5 to 95 %, non-condensing
Safety PCB flammability rating UL94-V-0
RoHS compliance EU directive 2002/95/EC
Dimensions ( Lx W x H) 98 x 78 x 17 mm (3.86 x 3.07 x 0.67 in)
Weight 61 g (0.134 lb)
Product identification
PCB Revision Written in copper on the PCB's backside
Serial Number IEEE registered MAC Address on barcode sticker label (Code 128C)

Ethernut 3 Support

Ethernut 3 is shipped with a pre-installed boot loader, that helps you to easily run own firmware or examples from NutWiki. How to do that and how to put Ethernut 3 into operation is explained in the Ethernut 3 Hardware Manual. Detailed information and instructions on how to to persistently install firmware images on Ethernut 3 can be found in the document Booting Ethernut 3.

To develop applications in Nut/OS, you should start reading Nut/OS on Ethernut 3, which explains how to configure and set up Nut/OS. The software manual describes the basic procedures of Nut/OS development. A detailed description of all OS functions can be found in the Online Reference API. The NutWiki provides an extensive collection of example code as well as further resources for developers.

Ethernut 3 is also equipped with a programmable CPLD. The tutorial Nut Programmable Logic describes the first steps. How to program the CPLD with Turtelizer 2 and OpenOCD is explained in Ethernut 3 CPLD.

All available documentation can be found on the Ethernut 3 page on


Ethernut 3 on
This document provides an outline on all available documentation for Ethernut 5

Ethernut 3.1 Hardware Manual
1.08 MB | English

AT91R40008 Datasheet
Datasheet for Ethernut 3’s CPU

Nut/OS on Ethernut 3
This document describes how to set up and run Nut/OS on Ethernut 3

Ethernut 3 CPLD programming
This documents desribes the programming of Ethernut 3’s CPLD

Ethernut 3 Memory Map
Default memory layout for Ethernut 3 after runtime initialization.

Ethernut 3 source code debugging
19.04.2011 | 2.90 MB | English

Nut/OS Software Manual
This document explains how to setup and use Nut/OS

Nut/OS Online Api
Online API reference for Nut/OS

The NutWiki offers programming resources for Nut/OS

Software and Tools

Nut/OS for Windows
Executable installation for Windows PCs.

Nut/OS for Linux and Mac OS X
Source code package for manual installation on Linux and Mac OS X.

Application Examples

Nut/OS Examples
The NutWiki provides a multitude of programming examples for Nut/OS