Sensor systems 2 AS-Interface

Issue date 2004-11-19 - Catalogue AS-Interface 2004/2005
FAULT
PWR
A D
Spec 2.1
Diagnostic function with peripheral error
AS-Interface - Introduction
Besides communications disturbances (i.e. erroneous messages), the master
can also detect hardware errors which occur on the slave. These peripheral
error messages can be used to power down systems in case of error,
since sensor signals may no longer be safely available. It is also possible
simply to evaluate stored data statistically in the master under "LFS" (list of
faulted slaves), in order to evaluate system safety. A red LED display is located
on the slave. This simplifies the location and correction of errors. An
extended diagnostic also makes it possible to locate even sporadically occurring
problems with configuration and communications and evaluate
them with the AS-i Control Tools. This information can be processed in the
PLC using the command interface and for instance then displayed in clear
text to the operator on a remote display.
Analogue transmission
The AS-Interface protocol allows the transmission of 4 bits in one cycle.
With the analogue profile S7.3, seven messages can be collected in the
master within only 35 ms, and output as a 16-bit analogue value. This was
only possible using an application program in specification 2.0. The output
of analogue control values as 0 V ... 10 V or 4 mA ... 20 mA signals is possible.
Extension of ID codes:
A/B slaves have ID codes = A hex , while standard slaves have a different ID
code of A hex . So as to distinguish the different profiles (types of slave), two
further identification codes were introduced, the ID1 code and the ID2 code.
The IO code and the ID2 code describe the profile of the A/B slaves completely
and are permanently stored in the slave.
Transfer rate and cycle time
The bit transmission rate of the AS-Interface is about 167 kBaud, in order
to make the system very resistant to cable reflexions and errors even with
complex topologies, while still eliminating the need for termination resistors.
The cycle time is, however, a deciding factor for small quantities of data.
When fully loaded, masters on specification 2.0 (31 slaves or 124 binary
sensors + 124 binary actuators) have a maximum cycle time of 5 ms, and
masters on specification 2.1 in extended mode (62 slaves, or 248 binary
sensors + 186 binary actuators) have a maximum cycle time of 10 ms. The
cycle time can be shortened by reducing the number of nodes or by addressing
A/B slaves in standard mode. Every unoccupied slave address
saves 150 µs. This makes the AS-Interface one of the fastest bus systems.
In a mixed system with standard slaves and A/B slaves, standard slaves are
interrogated on each cycle and A/B slaves every other cycle. On the nth cycle,
all A slaves are addressed, and on the n+1-th cycle, all the B slaves.
The master can use the configuration to detect which addresses are unoccupied
and doesn't interrogate these at all. If only one (either A or B) address
is assigned to an A/B slave on the AS-Interface network, then these
slaves are interrogated on every cycle. The frequency of interrogation can
be increased in this way.
Subject to reasonable modifications due to technical advances. Copyright Pepperl+Fuchs, Printed in Germany
Pepperl+Fuchs Group Tel.: Germany +49 621 776-0 USA +1 330 4253555 Singapore +65 67799091 Internet http://www.pepperl-fuchs.com
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