Introduction
Dec 2021
ATM60 / ATM90 / KHK53 17
Figure 4–3: Topology of Profibus DP
4.3.2 RS485 Transmission Technology
The ATMxx and KHK53 encoders with Profibus interface use RS485 transmission technology.
This is the most frequently used technology for Profibus DP, and is very easy to handle. The in-
stallation of the twisted pair cable does not require expert knowledge. The bus structure permits
the addition and removal of stations as well as step-by-step commissioning of the system, with-
out affecting the other stations concerned.
The transmission speed is between 9.6 KBits/s and MBits/s (selectable). During commission-
ing, the same transmission speed is selected for all devices on the bus (the encoders auto-
matically adjust).
Basic functions when using RS485 technology:
Network topology
• Linear bus, active bus termination at both ends.
• Stub lines are only permitted for baud rates ≤ 1.5 MBit/s.
Signal transmission
• NRZ (non-return to zero) format.
• 11 bits/character with: start, 8 x data, parity [even], stop.
Station numbers
• 32 stations in each segment without repeater[s].
• With repeaters: expandable to 127.
Connectivity
• 9-pin D-Sub connection plug (preferred).
• M12 round connector.
• Han-Brid plug acc. to DESINA recommendation.
4.3.3 Installation Notes re: RS485
All devices are connected in a line bus structure. Up to 32 stations (masters or slaves) can be
interconnected in a segment. At the beginning and end of each segment, the bus is terminated
using a terminating resistor. Trouble-free operation requires that the two bus terminations al-
ways be supplied with voltage.
For more than 32 subscribers, repeaters (line amplifiers) must be used to connect the individual
bus segments.
The encoders contain connectable bus terminations - (see DIP switch-n).
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