Bernecker + Rainer 5PC820.SX01-00, User Manual

Page: 55 / 318

Technical data • Entire device
Secti
on 2
Te
chn
ica
l da
ta
55 Automation PC 820 User's Manual V 1.20
RS485 interface operation
The pins of the RS422 default interface (1, 4, 6 and 9) should be used for operation. The pins
should be connected as shown.
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
resistance.
RS485 - Bus length and cable type
The maximum transfer rate of 115 kBit/s depends on the cable type being used.
The material used for the cable should preferably have all or most of the following properties in
order to reach an optimal transfer rate.
Figure 15: RS232/422/485 interface - operated in RS485 mode
Extension Transfer rate
1200 m Typically 115 kbits/s
Table 28: RS485 - Bus length and transfer rate
RS485 cable Property
Signal lines
Cable cross section
Wire insulation
Conductor resistance
Stranding
Shield 4 x 0.25 mm² (24AWG/19), tinned Cu wire
PE
≤
82
Ω
/km
Wires stranded in pairs
Paired shield with aluminum foil
Table 29: RS485 - Cable requirements
RXD
RXD
TXD
TXD
9
6
4
1
DATA
DATA