An AS-Interface network offers a cost-efficient alternative to conventional cabling at the lowest level of the automation hierarchy where it can operate stand-alone or with a controller. A network can also link into a higher level bus system for low-cost remote I/O. Continuous enhancements have broadened the applications base and today AS-Interface is proven in hundreds of thousands of products and applications spanning the automation spectrum.

At its simplest, AS-Interface is a digital replacement for traditional cable architectures. However, as you’ll discover, it can handle lots more as well and can be an important part of an automation hierarchy and strategy. It is especially suitable for lower levels of plant automation where binary field devices such as switches need to interoperate in a stand-alone local area automation network controlled by PLC or PC.

AS-Interface should not be compared with higher-level bus systems providing sophisticated performance at much higher cost! AS-Interface is tailored to the needs of devices such as sensors and actuators where low connection cost per node is critical and simplicity is paramount. Furthermore, established skills can still be utilized so AS-Interface ensures fast uptake and ready acceptance by existing operating and maintenance personnel. Many gateway products are now available, making AS-Interface ideal for interfacing field devices with higher-level bus systems. Ethernet links are also available, enabling an AS-Interface network to be controlled directly over a TCP/IP network.

AS-i Best Practices

1.)Layout for module bases and cables.

A. Bases –bases for modules/node/slaves should be placed on equipment first, according to machine print and distribution of I/O.

B. Cabling

  1. Yellow and Black cables should be laid out next , and affixed to module bases
  2. Always use the profiled yellow cable, brown for “+” and blue for “-.“
  3. Route the yellow cable away from power cables in conduit, cabletray, cable drag chain, and in control and satellite cabinets.
  4. Use 16 AWG conductors where possible inside panels and cabinets. Never use smaller than 18 AWG in any AS-I application.
  5. Maintain maximum separation distance inside panel between AS-I control components, and auxiliary power sources (DC or AC voltage), VFD’s, etc.
  6. Do not route AS-I control wiring or cables in the same channel, wire way or conduit as auxiliary power, DC or AC voltage.
  7. Each AS-i master/controller/backplane requires it’s own AS-i interface cable. AS-i cables must never be laid together, spliced, or otherwise connected
  8. Cables should then be connected to the AS-i Power Supply (powered “off”).

2.)Power Supplies

  1. Always use AS-i Power Supplies (PELV) with integrated data de-coupling, and connect ground (GND) with system ground
  2. Never connect an AS-i Power Supply to earth ground
  3. Connect AS-i yellow cable to powered “off” AS-i Power Supply, and make sure AS-i Power Supply is properly connected to AS-i master/backplane/gateway.
  4. Connect black cable to powered “off” auxiliary 24 VDC power supply or to auxiliary 24 VDC power terminals on AS-i Power Supply. If using a PLC backplane master, 24 VDC power is supplied from the PLC chassis.
  5. Power “on” 24 VDC power supply and then the AS-i Power Supply.

3.)AS-I Master

  1. Connect AS-I yellow cable, powered off (brown + & blue -) to appropriate terminals on AS-I master. AS-I master can be standalone controller, backplane master for PLC, or gateway to higher bus network.
  2. If using backplane master for PLC, AS-I master will configure as a standard card in the appropriate slot on the PLC. Typically, I/O is a direct map into input/output image tables.
  3. If using a standalone AS-I master/controller, or gateway, standard 24 VDC power must be provided to power electronics and processor. Connect 24 VDC to appropriate terminals on AS-I master.
  4. Power up system (AS-I power supply and 24 VDC power supply).

4.)Nodes/Modules/Slaves

  1. One of two options for adding nodes to the system
  1. Preaddress with handheld programmer prior to adding them to the AS-i network
  2. Place nodes/modules one at a time on the appropriate bases per machine print (Easy Start-up or Change Address under Address Slave menu, on Controller-e).
  1. Use each slave address only once. Either 1-31, or 1A through 31B for AS-i 2.1

5.)Network Expansion

  1. Without repeaters or extenders, the AS-i network must be no longer than 100m, including all branches of the “tree” topology.
  2. Additional lengths may be up to 100m with the addition of a repeater or extender and AS-i Power Supply.
  3. Up to two repeaters can be connected in series with AS-i Power Supplies for a maximum network length of 300m

6.)Sensors and Actuators

  1. Sensors and actuators must be supplied directly from the associated input or output of the slave.
  2. Cable lengths (patchcords) from the module to the I/O device should be as short as possible, and kept away from drive and motor cables. 5M patchcord typically the longest length applicable.

7.)Ensuring EMC immunity

  1. Do not install AS-I communication (yellow cable) together with power line in the same multi-conductor cable.
  2. Keep maximum distance between AS-I yellow cable and power cables.
  3. Maintain separation of DC control voltage from AC voltage components inside panels or cabinets, both in location and routing of wires and cabling.
  4. Connect all contactors, relays, solenoids, brakes, etc with appropriate “noise” suppression elements.
  5. Properly filter and ground all potential noise sources
  6. Always use shielded motor/drive cables and properly ground them

8.)System Diagnosis

  1. To locate network errors, the status and diagnosis bits can be evaluated at the PLC, or in the case of a higher bus system, at the gateway.
  2. Periphery fault information available on AS-I 2.1 masters and modules. Loss of auxiliary 24 VDC, Loss of communication with AS-I master, Short-circuit, & overloads covered under Periphery Faults.

9.)Interfacing with higher bus networks; Profibus, Devicenet, Ethernet gateways.

  1. Follow guidelines above for basic system set-up.
  2. Specific set-up instructions included with each ifm efector gateway. Instructions also available online at
  3. Load appropriate electronic files into PLC software (ex: GSD file into Profibus system software; EDS files for RSNetworx). GSD & EDS files available online at under part number search, data sheet, additional information.
  4. Program gateway to appropriate bus network address, via push buttons on gateway or via AS-I software.
  5. Configure communication “packet size” and baud rate for higher bus network, if necessary, via push buttons on gateway, or AS-I software.