Technical data • Individual components
Chapter 2
Technical data
Automation PC 510 User's Manual V 1.01
57
Image 11: RS232/422/485 interface - operated in RS485 mode
The RTS line must be switched each time the driver is sent and received; there is no automatic switch back. This
cannot be configured in Windows.
The voltage drop caused by long line lengths can lead to greater potential differences between the bus stations,
which can hinder communication. This can be improved by running ground wire with the others.
The line ends of the RS485 interface should (at least for longer line lengths or larger transfer rates) be closed.
Normally a passive terminator can be used on the bus ends by connecting each of the signal lines with 120 Ω
resistor.
RS485 - Bus length and cable type
The maximum transfer rate of 115 kbit/s depends on the cable type being used.
Extension
Transfer rate
1200 m
Typ. 115 kbit/s
Table 67: RS485 - Bus length and transfer rate
The material used for the cable should preferably have all or most of the following properties in order to reach an
optimal transfer rate.
RS485 cable
Property
Signal lines
Cable cross section
Wire insulation
Conductor resistance
Stranding
Shield
4x 0.25 mm² (24AWG/19), tinned Cu wire
PE
≤82 Ω/km
Wires stranded in pairs
Paired shield with aluminum foil
Grounding line
Cable cross section
Wire insulation
Conductor cross section
1x 0.34 mm² (22AWG/19), tinned Cu wire
PE
≤59 Ω/km
Outer sheathing
Material
Features
Cable shielding
PUR mixture
Halogen free
From tinned cu wires
Table 68: RS485 - Cable requirements
Terminating resistor
A RS485 TERM terminating resistor for the COM2 serial interface is already integrated on the I/O board. This
terminating resistor can be switched on or off with a switch located between the COM2 and COM1 serial interfaces.
An active terminating resistor is indicated by a yellow RS485 TERM LED.