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GOSSEN METRAWATT GMBH 6
1.3.2 RS-485 connection
When using a RS-485 interface, as many as 32 equipment (R2600/01 and others) can be connected to the bus.
Thereby, all terminals A, B and/or C are interconnected in parallel. The wiring must be made from equipment to equipment and must not be a star con-
nection. With longer bus lines (longer than about 5 m) the bus should be terminated at both ends with the characteristic impedance
(e.g. 200 Ω between A and B).
When using the 1799-V5040 interface converter on the master, the following pins are connected on the Sub-D plug:
A = 3 B = 8 C = 5
1.4 Principal function
Involved is a master/slave protocol with a fixedly assigned master (e.g. SPS) and as many as 255 slaves (equipment e.g. R2600/01).
Communication is in half-duplex mode.
An equipment connected to the master becomes active (responds) only, when
– it receives a valid telegram addressed to itself and
– the minimum specified response delay time (t
av) has elapsed so that the host computer has time to get ready to receive data.
Master R2600/01 R2600/01
A 21 21
B 20 20
C 19 19