Siemens IK PI · 2004
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AS-Interface
A/B technique
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Overview
The A/B technique concept
The AS-Interface specification 2.1 allows a doubling of network
stations from 31 to 62. The 31 addresses that can be assigned
in an AS-Interface network can be split into two mutually inde-
pendent sub-addresses, e.g. in 1A and 1B.
If this is utilized for all 31 slaves, up to 62 slaves can be con-
nected within an AS-Interface network. The so-called A/B slaves
can each have up to four inputs and three outputs.
Another new feature of the new AS-Interface specification V2.1
is integrated analog value transfer. In this case, integrated
means that no special function blocks are required in order to
access the analog values. Accessing data is therefore just as
easy in the case of analog values as it is with digital values. In-
tegrated analog value transfer can be used with analog slaves
that support Proifiles 7.3 and 7.4.
AS-Interface master
To operate A/B slaves in an AS-Interface network, master mod-
ules working according to the specification 2.1 must also be
used. The A/B technique is supported by the SIMATIC S7
masters and the DP/AS-Interface links from Siemens. To masters
that do not support specification 2.1, only standard and A slaves
can be connected.
The sub-address of A/B slaves is set to “A” by default.
Masters and slaves that are already working to the new specifi-
cation are identified accordingly in the catalog.
Addressing A/B slaves
A/B slaves can be addressed like standard slaves via all com-
mercial AS-Interface addressing units conforming to specifica-
tion 2.1. AS-Interface addressing units that do not conform to the
new specification 2.1 can readdress A/B slaves only as A slaves.
As far as addressing is concerned, an analog slave is like a stan-
dard slave. Up to 31 analog slaves can therefore be operated in
one AS-Interface segment.
Communication cycle
Standard slaves are polled in every cycle (max. cycle time:
5ms).
If only an A or B slave is installed at an address, this slave is also
polled in every cycle (max. cycle time: 5 ms).
If an A/B slave pair is installed at an address, slave A is polled in
one cycle, slave B in the next (max. cycle time: 10 ms).
If only standard and/or A slaves are installed in a network, the
cycle time is the same as for standard masters (max. cycle time:
5 ms).
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Benefits
•Lower costs for masters and powe r supply units
•Enhanced decentralization in instal lations with numerous,
widely distributed signals
•Existing AS-Interface systems ca n be expanded further
G_IK10_XX_20020
Previously 31 nodes Slave 1
with A/B slaves max. 62 nodes:
Mixed operation also permissible:
Slave 31
Slave 1A Slave 31B
Slave 1 Slave 31
Slave 1B Slave 31A
Slave 2A Slave 2B
Slave type Number of slaves Number of inputs Number of outputs
AS-Interface standard Standard slave Up to 31 31 x 4 = 124 31 x 4 = 124
AS-Interface version 2.1 A/B slave Up to 62 62 x 4 = 248 62 x 3 = 186