Siemens MICROMASTER 440 Operating Instructions Manual page 153

Issue 10/06
Fig. 3-44
The two ends of a bus line (first node and last node) must be terminated with bus
terminating networks. (refer to Section 3.7.1.3). Point-to-point connections are
handled just like bus connections. One node has the master function and the other
has the slave function.
Data is transferred in accordance with Standard EIA 485. RS 232 can be used for
point-to-point links. Data transfer is always half-duplex − i.e. alternating between
transmitting and receiving − and it must be controlled by the software. The half-
duplex technique allows the same cables to be used for both data-transfer
directions. This permits simple and inexpensive bus cabling, operation in
environments subject to interference and a high data transfer rate.
A shielded, twisted two-wire cable is used as the bus cable.
Table 3-16
Conductor diameter
Conductor
Lay ratio
Overall shield
Overall diameter - ∅
External sheath
NOTE
All information should only be considered as a recommendation.
Deviations or different measures may be required depending on the particular
requirements, the specific application and the conditions on site.
MICROMASTER 440 Operating Instructions
6SE6400-5AW00-0BP0
Slave Slave
First node
USS bus topology
Structural data
Master
Maximum 32 slaves
2 x ≈ 0,5 mm2
≥ 16 x ≤  0 ,2 mm
≥ 20 twists / m
Braided, tin-plated copper wire, diameter
85 % optical coverage
5 mm
Depending on the requirements regarding flame retardation,
deposits after burning etc.
3 Functions
Slave
Last node
∅ ≥
1,1 mm2
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