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PROFIBUS Networks
5 RS 485 Repeater
5.1 Application of the RS 485 Repeater
What is an RS 485 Repeater?
An RS 485 repeater amplifies data signals on LAN cables and connects bus segments.
Using the RS 485 Repeater
You require an RS 485 repeater in the following situations:
â When there are more than 32 stations connected to the bus
â When electrically isolated bus segments are required or
â When the maximum cable length of a segment (standard LAN cable) is exceeded (see Table 5.1).
Transmission Rate Maximum Cable Length of a Segment (in m)
9.6 to 93.75 Kbps
187.5 Kbps 800
500 Kbps 400
1.5 Mbps 200
3 to 12 Mbps 100
Table 5.1: Maximum Cable Length of a Segment (Standard LAN Cable)
1000
Rules
If you want to install the bus with RS 485 repeaters, the following rules apply:
â A maximum of 9 RS 485 repeaters can be connected in series.
â The maximum cable length between two nodes must not exceed the values in Table 5.2:
Transmission Rate Maximum
(in m) with RS 485 Repeaters
9.6 to 93.75 Kbps
187.5 Kbps 8000
500 Kbps 4000
1.5 Mbps 2000
3 to 12 Mbps 1000
Cable Length Between T
10000
wo Nodes
Table 5.2: Maximum Cable Length Between Two Nodes (Standard LAN Cables)
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L+ M PE M 5.2
À
Â
A1
B
A1 B1
RS 485-REPEA
TER
Ç
5.2 Appearance of the RS 485 Repeater (6ES7 972-0AA00-0XA0)
Appearance of the RS 485 Repeater
Table 5.3 shows the elements of the RS 485 repeater:
Front View of the Repeater No. Function
À Terminal for connecting the power supply of the RS 485 repeater (pin
”M5.2” is the reference ground if you want to measure the voltage
DC
24
V
24
V
L+ M PE M 5.2
À
Á
Â
A1B1A1 B1
1
ON
È
PG
OP
Ã
Ä
Å
ON
SIEMENS
RS 485-REPEA
A2
B2A2 B2
TER
Æ
Á
Ç
between terminals ”A2” and ”B2”).
Á Shield clamp for strain relief and grounding the LAN cable of bus
segment 1 or bus segment 2
 Terminal for the LAN cable of bus segment 1
à Terminating resistor for bus segment 1
Ä Switch for transmission rate
the settings are as follows:
0: Bus segments not connected 5: 500 Kbps
1: 9.6 Kbps 6: 1.5 Mbps
2: 19.2 Kbps 7: 3 Mbps
3: 93.75 Kbps 8: 6 Mbps
4: 187.5 Kbps 9: 12 Mbps
Å Terminating resistor for bus segment 2
Æ Terminal for the LAN cable of bus segment 2
Ç Catch for mounting and removing the RS 485 repeater on a standard
rail
È Interface for PG/OP on bus segment 1
PROFIBUS Networks
Table 5.3: Description and Functions of the RS 485 Repeater
+ Terminal M5.2 of the power supply (see Table 5.3,À) is used as the reference ground for signal
measurements if problems occur and must not be wired up.
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Technical Data
Table 5.4 shows the technical data of the RS 485 repeater:
Technical Data
Power supply
– Rated voltage
– Ripple
Power consumption at rated voltage
– Without load on the PG/OP connector
– Load on the PG/OP connector (5 V/90 mA)
– Load on the PG/OP connector (24 V/100 mA)
Electrical isolation yes, 500 V AC
Redundant mode no
Transmission rate 9.6 Kbps to 12 Mbps
Degree of protection IP 20
Dimensions W H D (in mm) 45 128 67
Weight (including packing) 350 g
24 V DC
18 V to 30 V DC
100 mA
130 mA
200 mA
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Table 5.4: Technical Data of the RS 485 Repeater
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5
9
8
2
1
Pinout of the Sub D Connector (PG/OP Connector)
The 9-pin sub D connector has the following pinout:
Layout Pin No. Signal Name Meaning
1 – –
5
4
3
7
2
6
1
2 M24V Chassis 24 V
3 RxD/TxD-P Data line B
4 RTS Request To Send
5 M5V2 Data reference voltage (of station)
6 P5V2 Power plus (from station)
7 P24V 24 V
8 RxD/TxD-N Data line A
9 – –
PROFIBUS Networks
Table 5.5: Pin Assignment of the 9-Pin Sub D Connector PG/OP Connector
Block Diagram
Figure 5. 1 shows the block diagram of the RS 485 repeater:
â Bus segment 1 and bus segment 2 are electrically isolated.
â Bus segment 2 and the PG/OP connector are electrically isolated.
â Signals are amplified:
â between bus segment 1 and bus segment 2
â between the PG/OP connector and bus segment 2
Segment 1
A1
B1
A1
B1
Logic
Segment 2
A2
B2
A2
B2
1M1M
L+ (24 V)
M
PG/OP
socket
L+ (24 V)
5V
24V
5V
24V
M
A1
B1
5 V
PE
M 5.2
M5 V
Figure 5. 1: Block Diagram of the RS 485 Repeater
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PROFIBUS Networks
5.3 Possible Configurations with the RS 485 Repeater
Overview
The following section shows the configurations in which you can use the RS 485 repeater:
â Segment 1 and Segment 2 terminated on the RS 485 repeater
â Segment 1 terminated on the RS 485 repeater and Segment 2 connected through on the RS 485 repeater
â Segment 2 terminated on the RS 485 repeater and Segment 1 connected through on the RS 485 repeater
â Segment 1 and Segment 2 connected through on the RS 485 repeater
Terminating Resistor On/Off
Figure 5. 2 shows the setting for the terminating resistor:
Terminating Resistor
On:
Figure 5. 2: Setting of the Terminating Resistor
Terminating Resistor
Off:
Segments 1 and 2 Terminated
Figure 5. 3 shows how to connect the RS 485 repeater to the ends between two segments:
Segment 1
Segment 1
Terminate bus
segment 1
R
Segment 2
Segment 2
Figure 5. 3: Connecting Two Bus Segments to the RS 485 Repeater (1)
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Terminate bus
segment 2
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PROFIBUS Networks
Segment 1 Terminated, Segment 2 Connected Through
Figure 5. 4 shows the connection between two segments via an RS 485 repeater with one segment connected
through:
Segment 1
Segment 1
Terminate bus
segment 1
R
Segment 2
Do not terminate
bus segment 2
Segment 2
Figure 5. 4: Connection of Two Bus Segments on the RS 485 Repeater (2)
Segments 1 and 2 Connected Through
Figure 5. 5 shows the connection of two segments via an RS 485 repeater with both LAN cables connected
through on the repeater.
Segment 1
Segment 1
R
Segment 2
Segment 2
Figure 5. 5: Connection of two Bus Segments on the RS 485 Repeater (3)
Do not terminate
bus segment 1
Do not terminate
bus segment 2
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PROFIBUS Networks
5.4 Installing and Uninstalling the RS 485 Repeater
Overview
You can install the RS 485 repeater as follows:
â On a rail for S7-300
or
â On a standard rail (DIN EN 500 22-35x7.5)
Installation on a Rail for S7-300
To install the RS 485 repeater on a rail for S7-300s, the catch on the rear of the RS 485 repeater must first be
removed (see Figure 5. 6):
1. Insert a screwdriver below the tongue of the catch (1) and
2. Push the screwdriver towards the rear of the module (2). Hold the screwdriver in this position!
Result: The catch is released from the RS 485 repeater.
3. With your free hand lift the catch up as far as it will go and then remove the catch (3).
Result: The catch is removed from the RS 485 repeater.
4. Fit the RS 485 repeater onto the rail for an S7-300 (4).
5. Push it towards the back as far as it will go (5).
6. Tighten the securing screw with a torque of 80 to 110 Ncm (6).
Rear view: Front view:
4
2
1
3
5
6
Figure 5. 6: Installing the RS 485 Repeater on a Standard Rail for an S7-300
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80 to 110 Ncm
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Removing the Repeater from an S7-300 Rail
To remove the RS 485 repeater from the S7-300 rail:
1. Undo the screw securing the RS 485 repeater (1) and
2. Pull the RS 485 repeater out and up (2).
PROFIBUS Networks
1
Figure 5. 7: Removing the RS 485 Repeater from the S7-300 Rail
2
Installation on a Standard Rail
To be able to install the repeater on a standard rail, the catch must be present on the back of the RS 485 repeater:
1. Fit the RS 485 repeater on to the standard rail from above and
2. Push it towards the back until the catch locks it in place.
Removing the RS 485 from the Standard Rail
To remove the RS 485 repeater from the standard rail:
1. Press down the catch on the bottom of the RS 485 repeater using a screwdriver and
2. Pull the RS 485 repeater out and upwards to remove it from the standard rail.
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PROFIBUS Networks
5.5 Ungrounded Operation of the RS 485 Repeater
Ungrounded Operation
Ungrounded operation means that chassis and PE are not connected.
The ungrounded operation of the RS 485 repeater allows you to operate electrically isolated bus segments.
Figure 5. 8 shows the change in the potentials resulting from using the RS 485 repeater.
Signals
ungrounded
Signals grounded
Figure 5. 8: Ungrounded Operation of ET200 Bus Segments
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PROFIBUS Networks
5.6 Connecting the Power Supply
Cable Type
To connect the 24 V power supply, use flexible cables with a cross section of 0.25 mm2 to 2.5 mm2 (AWG 26 to
14). Use suitable wire-end ferrules for the wire cross section.
Rules for Cabling
Appendix D contains detailed information about cabling.
Connecting the Power Supply
To connect the power supply of the RS 485 repeater:
1. Strip the insulation from the wire for the 24 V DC power supply.
2. Connect the cable to terminals ”L+”, ”M” and ”PE”.
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PROFIBUS Networks
5.7 Connecting the LAN Cables
Connect the PROFIBUS LAN cable to the RS 485 repeater as follows:
1. Cut the PROFIBUS LAN cable to the required length.
2. Strip the insulation from the PROFIBUS LAN cable as shown in Figure 5. 9.
The braided shield must be folded back on to the cable. Only then can the shield clamp serve as strain relief
and as the shield contact.
6XV1 830–0AH10 Standard LAN cable
6XV1 830–0BH10 LAN cable with PE sheath
6XV1 830–3BH10 Trailing cable
6XV1 830–3CH10 LAN cable for festoons
8,5 16 10
6XV1 830–3AH10 Underground cable
16 1016
8,5
Braid shield must be folded back!
Figure 5. 9: Lengths for Stripping the Cable to Connect it to the RS 485 Repeater
3. Connect the PROFIBUS LAN cable to the RS 485 repeater:
Connect the same wires (green/red for the PROFIBUS LAN cable) to the same terminal A or B (in other
words always connect Terminal A with a green wire and Terminal B with a red wire or vice versa).
4. Tighten the shield clamps so that the shield makes good contact with the clamp.
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