AS-Interface History

AS-Interface was developed during the late 1980 and early 1990 by a group (consortium) of 11

companies mostly known for their offering of industrial non-contact sensing devices like inductive sensors, photoelectric sensors, capacitive sensors and ultrasonic sensors. Once development was completed the consortium was resolved and a member organization, AS-International, was founded. The first operational system was shown at the 1994 Hanover fair (Hannover Messe or Hannover Fair).

Original Specification (1994, Version 2.04)
      In its original form the network was capable of supporting up to 31 binary I/O devices/modules, where each device could exchange 4 bit of input and 4 bit of output data, resulting in a total of 124 inputs and 124 outputs on a single network. Important features like Automatic Single Node Replacement were already part of the system. The network update time is easily calculated by multiplying the number I/O nodes with the deterministic update time for each node (approximately 150 microseconds), for a maximum update time of 5 ms. This simplified calculation does not include the Management Phase which is negligible for typical installations. It does also not include any communication retries.



Enhancements (1998, Version 2.11) Following its introduction users quickly adopted AS-Interface, driving the demand for additional functionality and features. As a consequence, these demands were addressed with certain specification enhancements allowing the creation of analog input/output devices and increasing the number of possible binary I/O devices to 62. Diagnostics functionality was also enhanced by the creation of the Peripheral Fault Bit. In order to retain full forward and backward compatibility, the size of the data frame exchanged between the network master (Scanners and Gateways) was not increased. Instead, one of the four output bits was used to select between the so-called A and B nodes. This enabled each of the 31 addresses to be used twice. The address space was increased to 1A to 31A plus 1B to 31B. As a consequence of using an output bit as the A/B selector, the fourth output bit was not available to the user and binary I/O nodes built to this profile offered a maximum of 4 inputs and 3 outputs, increasing the total amount of I/O on a single network to 248 inputs and 186 outputs. The maximum update time of a fully loaded network is 10 ms.

Additional capabilities (2005/2007, Version 3.0) By 2005 it became necessary to address additional user requirements. Also, the increased usage of Ethernet based industrial protocols called for a low level solution that overcame the inherent shortcomings of Ethernet (e.g. restricted topology, large data frame, costly usage of switches ...) This specification addressed the users requirements by defining new communication profiles for binary and analog data plus the introduction of a serial data transmission profile. The following is an incomplete list of the new capabilities

•  Binary I/O nodes supporting A/B addressing with 4 Inputs and 4 Outputs
•  Binary I/O nodes supporting A/B addressing with 8 Inputs and 8 Outputs 
•  Configurable (8, 12 or 16 bit) fast analog channel 
•  Full Duplex bit serial data channel

 With these new capabilities, AS-Interface becomes the ideal partner network for any of the currently available Ethernet based industrial protocols. Gateways to EtherNet/IPTM, PROFINET, Modbus/TCP, SERCOS III and others are available. Some controls experts have voiced the opinion that within the next 10 years networking solutions positioned between AS-Interface and Ethernet will not be used in any new installation.[citation needed] In a worst case scenario, using 62 nodes with 4 inputs and 4 outputs each the update time is 10 ms for the inputs and 20 ms for the outputs.