26
akytec GmbH - Vahrenwalder Str. 269 A - 30179 Hannover - Germany Tel.: +49 (0) 511 16 59 672–0 - www.akytec.de
6.3 RS485 network
RS485 standard is used for data exchange. The RS485 serial interface is based on two-wire
technology and half-duplex mode. The protocols Modbus RTU and Modbus ASCII are supported.
Devices are connected to a network according to linear (bus) topology. It means that the line goes
from the first device to the second one, from the second one to the third one, etc. Star connections
and spur lines are not allowed. The maximum distance between the first and last device along the
line is 1200 m.
The network consists of a master device and can contain up to 32 slave devices. The number of
slave devices and the network length can be increased using a RS485 interface repeater.
Line reflections always occur at the open bus ends (the first and the last node). The higher the data
transmission rate, the stronger they are. Terminating resistors on the both ends of line can be useful
to minimize reflections. Terminating resistors of 120…150 Ω, 0.25 kW are recommended.
Fig. 6.4 RS485 network
Shielded twisted pair cable for RS485-bus is recommended. Maximum cable length is 1200 m.
Connect the RS485 lines to terminals D+ and D-.
6.4 Quick replacement
The device is equipped with plug-in terminal blocks which
enable quick replacement of the device without disconnecting
the existing wiring (
).
To replace the device:
1. Power off all connected lines including power supply.
2. Remove all detachable parts of the terminal blocks.
3. Replace the device.
4. Connect detachable parts with existing wiring to the device.
Fig. 6.5 Terminal block
replacement
