15/11/05 - Article - AS-Interface Version 3.0 - Pacesetter for the automation




AS-Interface Version 3.0

Pacesetter for the automation


The pacesetter sets the speed in automation as well as in the field of sports. Now, AS-Interface's latest V3 specification has increased the pace once more, offering more power and flexibility too. All the well-known advantages of AS-Interface are retained, particularly ease of use and openness.
Speed of transmission of the different AS-i profiles



AS-Interface began with a simple idea: to create a networking system for the simplest sensors and actuators.
Global success has come through easy installation, easy operability, excellent cost-effectiveness and openness, together with good compatibility with other fieldbuses.
The author, Bernhard Wiedemann of Bihl+Wiedemann is member of the Technical Commission of AS-Interface

AS-Interface Version 3.0: faster and more flexible

AS-Interface has been continuously enhanced since its inception. The previous specification – version 2.11 – allowed the number of slaves on a network to be doubled and introduced the transmission of analog values too. In defining the new version 3.0, speed and flexibility (among others) have played an important role.

This list now being expanded by the latest AS-Interface specification, which offers, for example, new diagnostic functions such as the ability to recognize duplicate addresses. The new slaves also monitor themselves, and the latest AS-i Analyser from Bihl+Wiedemann provides, with just one click, a 'fitness- check' for the whole system.

Figure: A Master of the youngest Master Generation:
AS-i/PROFIBUS Gateway
The profile group 'Combined Transaction Type 4' is a good example – it's a logical progression from Type 1 Profiles, S-7.3 and S-7.4, which were defined in 1999 to allow easy transmission of analog values. The integration of this profile into AS-Interface was a good solution because most analog sensors only need low power and are therefore perfectly suited to use with AS-i (data and power on the same line).

With Type 1 Profiles, analog data could be handled as easily as binary values. Type 4 profiles introduce universal application and higher speeds.




Profile S-7.A.9 is an interesting variant which is characterized by the following:
  • 1 or 2 channel input modules, adjustable over the handheld adressing device
  • 12 or 14 bit
  • A/B slave
  • Only 3 cycles/channel for 12 bit
The second channel can be switched by the user without being forced to configure anything in the controller, It is enabled via the ID1-Code of the slave, and defined using a handheld addressing device. The number of the bits to be transmitted can also be adjusted; up to 4 times the resolution can be achieved with only a 33% increase in transmission time.

Figure: The new AS-i Analog Module transmits input and output signals in one AS-i cycle – without additional expenses or loss of time.

New records can be set with new Slave Profiles

In this way 62 modules and two 12 bit analog channels can each be collected in just 60 ms. If one channel only is used the cycle time is halved. But even higher speeds are possible. Take the example of an AS-i network comprising single channel slaves according to S-7.A.9.		 If the B addresses remain unused, every slave is addressed in every cycle. The cycle time can then be calculated as follows: 10 Slaves + activation phase + management phase x 150 Micro- seconds (µs) = 1,8 ms. So, 5,4 ms are sufficient for 10 analog values at 12 bit resolution. Using 3 slaves the cycle time is 2,25 ms – which should be adequate for nearly all applications!

However, even this can be exceeded using the new profile group Type 5, which has 2 to 4 AS-i Slaves in one analog module. Here, the concept is simple and powerful:
  • 1 channel input plus 1 channel output
  • from 2 up to 4 single addresses per module
The input and output signals are always transmitted together in one AS-i cycle without additional work and without losing time. So, Type 5 Profile S-6.0.x actually beats the results calculated for Type 4 Slaves S-7.A.9..

Speed is not the result of witchcraft

These transmission speeds have nothing to do with witchcraft but depend on sophisticated technology, and the continuous development of an already powerful networking system. Fortunately, the user does not have to be involved in the technicalities because AS-i also means 'plug and play'.
 



Article as PDF file

The article appeared in AS-i Magazin, issue 2/2005

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