Connection And Connection Assignment Of Rs 485 - Pepperl+Fuchs KFD2-HMM-16 Manual

2.1.13

Connection and Connection Assignment of RS 485

Connector assignment of the removable terminals:
Terminal
13, 19
14, 20 RxD/TxD + (RS 485 B)
15, 21 RxD/TxD - (R S485 A)
If the screen is grounded, the grounding should only be connected to one end of the cable, in
order to avoid equipotential bonding currents. However, in all cases, existing guidelines and
regulations must be observed.
To connect a standard PC with a R S232 interface an interface converter R S485 to R S232 is
required. A converter that has been tested and recommended by Pepperl+Fuchs is manufactu-
red by Telebyte (Telebyte Model No. 285). This can be obtained from Pepperl+Fuchs under the
part number "Telebyte Model 285M".
In accordance with the RS 485 specification up to 32 stations ("multidrop") can be connected to a up to
1200 m cable (for data rates less than 100 kBaud). Pepperl+Fuchs recommends that this length of cable is
not exceeded. Even though problems seldom occur at these data rates, screened twisted two-wire cabling
should be used.
In addition a terminating resistor should be connected to each end of the R S485 cable. If the multiplexer
master is such a device, i. e. the RS 485 cable ends here and is not routed to other devices, then the second
available connection terminal for the RS 485 can be used for the connection of a terminating resistance.
The terminating resistor terminates the cables with its characteristic impedance. At minimal baud rates and
with short lengths of cable, in practice quite often no terminating resistors are used. If communication errors
arise, or if these are to be positively excluded from the outset, terminating resistors typically of
120 Ω ... 220 Ω should be used. Such can, for example, be connected between terminals 20 and 21.
If an interface converter is used, a terminating resistor should be connected to the converter
and another to the other end of the cable.
Subject to reasonable modifications due to technical advances.
14
Pepperl+Fuchs Group • Tel.: Germany (06 21) 7 76-0 • USA (330) 4 25 35 55 • Singapore 7 79 90 91 • Internet http://www.pepperl-fuchs.com
Description
Screen
RS 485 differential signal
HART Multiplexer Master KFD2-HMM-16
Meaning
Cable screening
Product description
Copyright Pepperl+Fuchs, Printed in Germany