This page is updated August 5th 2010 and optimized for 1280x1024 pixels.
It is only available in English.

Welcome to the official home page for the Max-i fieldbus
and Max-i Association.

Overview

Max-i is a new, very cheap, but extremely powerful fieldbus, which enables the lowest total automation costs ever seen combined with maximum performance! It may be regarded as a combination between a highly improved CAN bus and a 12-V power supply and may for example be used for industrial automation, building automation, automotive applications and stage light control.

The name Max-i means Multiple Access Cross-coupled interface. It refers to Max-i being an event driven multi-master bus, which for industrial applications uses standard "green" installation cables connected as a balanced 4-wire line. For applications in cars and homes, it is also possible to use an unbalanced cable with 3, 2 or even a single conductor. The name also refers to the properties, which in most cases by far exceed comparable fieldbus systems.

Cheap single-chip solution
for ALL applications

With Max-i, it is possible to make a complete bus interface in one, small (3 to 8-pin) integrated circuit (IC), which is easy to build into even the smallest and most price sensitive actuator or sensor, gets its supply voltage of 12 V directly from the bus and doesn't need any other components than a decoupling capacitor over the supply voltage rails. This not only saves the traditional distributed coupling boxes and a lot of cabling, but also the expensive and time consuming conformance tests, which are required by most other fieldbus standards. It also makes it possible to do with only one bus in automotive applications because Max-i is as cheap as LIN, more powerful than CAN, as deterministic as TTCAN (Time Triggered CAN) and for a given amount of money, it offers the same speed and much higher safety than FlexRay and its predecessor Byteflight. For emergency data like airbag firing, Max-i can offer high priority, 100% hardware based communication with a response times in the order of 100-200 microseconds, which is faster than FlexRay, and due to the very low cost, high amounts of data can just be transferred on more busses, which simultaneously increases the failure tolerance.

Simple, but Powerful

Max-i combines the outstanding performance with a beautiful simplicity. There are no complicated object models or connection sets and no device profiles or control profiles - just a few registers to setup and a new numbering systems - PNS, which allows the various process values to be addressed directly as properties of the equipment to which they belong like for example HX127AT4 for Heat Exchanger 127A Temperature 4. The Max-i specification fills only approximately 100 pages where approximately half is used for background material and annexes. As a comparison, most other fieldbus systems have specifications way over 1000 pages, which requires several months to study and implement. The specification can be downloaded from this page and used free of charge for all non-commercial use. Commercial use requires membership of Max-i Association.

450 W Power Transfer

With Max-i, it is possible to connect several thousand devices to one bus, and unlike any other fieldbus it has power enough to drive them all. The use of installation cables instead of communication cables makes it for example possible to transfer power up to 450 W on 6 mm² cables. Because the cable is not shielded, the traditional dilemma with the shield connection is avoided. For the sake of noise immunity, a shield must be connected to ground/chassis in both ends, but it is simultaneously a very bad idea to establish potential equalization between different parts of the plant through a thin fieldbus cable - especially in plants, which use a TN-C net with a common neutral and protective earth where the current in such a connection can easily be over 10 A (20 A has been measured in a water pipe)! Nevertheless, it is common practice with almost all other fieldbus systems!

As Max-i may be regarded as a 12 V supply with advanced communication, it will also be extremely suited as a supplementary power supply and control in the houses of the future. All Boolean outputs may be divided in up to 255 groups, which may be switched off in three steps for example during lunch breaks, when you leave a building or an case of failing "green" energy supply or a heavily loaded power net. Calculations done by the Danish engineering company Rambøll shows that such a supply can save the Danish households in the order of 1 billion Danish kroner per year corresponding to approximately $200,000,000, and you will get rid of all the clumsy and often inefficient converter boxes to portable computers, mobile phones etc.

Highly Improved CAN

Max-i may also be regarded as a highly improved CAN. In the same way as CAN, it uses the very efficient producer/consumer model, and it also has two different identifier lengths of 12 and 31 bits corresponding to the 11 and 29 bit of CAN. Max-i is able to run all CAN protocols with very small adjustments, but in practice, it is not necessary with an extra layer of software as also level 6 of the OSI model is defined with standard data types and setup attributes. In this way, the problem with incompatible dialects like CANopen, DeviceNet and SDS is avoided, and if PNS is used, it is not even necessary with any cross-reference tables. This saves a lot of work.

The maximum bus length can be up to 8 km in linear bus topology and 16 km in a closed ring - without repeaters! At that length, Max-i can transfer approximately 70 single process values per second, but this number is increased to approximately 10,000 at a linear bus of 50 m - even if the values are polled. In Max-i it does not take longer time to poll a value than to transmit it event driven as the first and last part of the telegram is just transmitted by two or more devices. Because of a special local/global bit in the identifier, it is also possible for a SCADA system to poll values from a fast data stream without being overloaded.

Most process values use 2, 18 or 34 bits, and it is possible to change a value temporary, which can save a lot of time during commissioning. Max-i can also send 16- and/or 32-bit values to up to 256 devices in one telegram, which gives an even higher efficiency and ensures 100% data synchronization for example for positioning systems and for stage light control where Max-i with advantage can replace DMX512. Unlike CAN, which can only transfer 8 bytes, there are no limitations on the telegram length except for a selectable watchdog, which may limit the data length to 516 bytes.

Outstanding Safety

Max-i is from the start designed to be able to fulfill IEC 61508 SIL 3 for person safety - without additional layers! For example, it uses a 22-bit CRC check, the identifier is protected against masquerading by a 7-bit Hamming code, the telegrams may use an 8-bit rolling serial number and the entire signal processing is done in hardware, which is much safer and much more predictable than any software solution. There is also "babbling-idiot" protection so that all telegrams always will come through regardless of a very talkative device with high priority. Unlike CAN, Max-i is therefore fully deterministic and has a predictable response time. Max-i may therefore also replace time triggered CAN (TTCAN), which is rather slow and very inflexible.

In Max-i, the traditional termination resistors have been replaced by multi diode clamps in each device. This gives a very high failure tolerance even without multiple communication lines as the bus may be cut in as many parts as there are power supplies, and each part will still work! A closed ring with a length less than half the maximum length can be cut at any place without any loss of communication.

Excellent Noise Immunity

For several reasons, Max-i has an excellent noise immunity:

• The diode clamps reduces the power loss in the line termination to approximately the half compared to termination resistors and they utilize the reflections to improve the signal waveform and prevent bias-distortion due to noise rectification.

• There is no bias-distortion due to bit coding. Each bit consists of a pause, which can be 0, followed by a pulse with fixed length, which inverts the line state. This gives a DC-free, self-clocking code with substantial higher efficiency than for example Manchester coding, and it simultaneously ensures that there is never any bias distortion even in case of heavy capacitive loading. Where CAN becomes extremely critical at long cable lengths and suffers from a heavy bias distortion coursed by the NRZ coding, the asymmetrical line driving and overlapping pulses, Max-i preserves its timing margin and signal integrity.

• Because of the high communication voltage of approximately 11 V and the very low characteristic impedance of the 4-wire line of 40-50 ohm, the transmitter power is approximately 6 W for devices mounted in the middle of the line. This is approximately 30 times more than CAN or RS-485 based systems and approximately 300 times more than IEC 61158-2 based systems! In spite of the very high transmitter power, the radiated emmission (EME) is very low because of the balanced line and the special bit coding with varying pause and scrambling, which courses a spread-spectrum effect.

• The receiver hysteresis is 4 V (at a supply voltage of 12 V). This is approximately 25-50 times more than CAN or RS-485 based systems.

The excellent noise immunity makes it possible to draw the cable in the same cable ducts as for example telephone cables, power cables and cables from frequency converters without the usual restrictions of a minimum distance and crossing in right angles. This saves a lot of money for mounting.

Evaluation Board

Until the final IC solution is available, Innovatic can offer an evaluation board - EB1, which simulates an 8-pin IC solution by means of an FPGA and other standard components. This solution may be very interesting for vendors, who want to be at the front edge of the development and have a possibility to influence the standard before the IC is made.

Vendors, who want to utilize the outstanding properties of Max-i and embed this preliminary Max-i interface directly into their products, can buy the pre-programmed FPGA from Innovatic (or through Actel), which simultaneously grants the vendor a royalty free, non-exclusive right to use the schematic of the evaluation board and the PCB layout. In this way, it is not necessary to wait for the final IC! As the interface does not need any microprocessor assistance, it is not more expencive that most other fieldbus interfaces and may therefore be used for example for distributed I/O, but of course, Max-i will not release its potential of very low cost and very small size before the IC is ready.