Sensor systems 2 AS-Interface

AS-Interface - Introduction
16
62
Spec 2.1
1.4 AS-Interface specification 2.1
Functional description of the
AS-Interface specification 2.1
With the AS-Interface specification 2.1, which was defined in 1999 by the
AS-Interface Association as a backwards-compatible extension retaining
the protocol and physical parameters, significant advantages for the user
were introduced:
Number of nodes increased from 31 standard slaves to
62 A/B slaves,
enhanced diagnostic function with peripheral error bit,
simple analogue value transmission with internal data handling,
extension of the ID codes of the nodes.
Devices in accordance with specification 2.1 are denoted on data sheets
with this symbol.
62 nodes on AS-Interface network
To take advantage of these possibilities, a VB... Master/Gateway is needed.
Standard slaves (as in specification 2.0), thanks to backwards compatibility,
can still be connected to a new master using specification 2.1. However,
two of the 62 possible addresses are occupied by one standard slave. The
use of A/B Slaves on an "old" master is possible, by always setting the select
bit to logical "0". Despite this, we don't recommend it, since a change to
this bit will change the address, and it may thus be impossible to talk to the
slave due to such a configuration error.
The master message is almost unchanged in the specification 2.1. The only
change is that the select bit "SEL" is transmitted in what used to be the
fourth output bit "I3", which in addition to the address bits A0 ... A4 enables
the extended A/B addressing.
Each address can therefore be split into A and B addresses, i.e. in addresses
15A and 15B.
Since the fourth output bit is now used as an additional address bit, only 3
output bits per slave can now be transmitted, that is, per AS-Interface network
3* 62 = 186 output bits are set. The slave response remains unchanged,
and there are now 4 * 62 = 248 bits of input data available.
Standard slaves can easily be used with a "new" VB... master, however, the
following changes apply:
A standard slave occupies both A and B addresses and thus reduces the
maximum number of nodes by one.
Standard slaves on a "new" VB... master/gateway are recognised using
the identification code (ID code) and can still have 4 output data bits.
Analogue modules and safe modules occupy a full address, even if these
devices are designed to specification 2.1. This allows the response time of
these modules to be kept to a minimum.
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
Issue date 2004-11-19 - Catalogue AS-Interface 2004/2005