ABB TPU2000 Technical Manual page 371

2. Termination must be attached to the extreme ends of the cable. If ABB relays are at the extreme ends of the
cable, internal termination resistors are available to provide termination. If the TELEBYTE converter is
inserted at the end of the cable, Switch Bank 2, Dipswitch position 1 inserts or removes a 120 ohm resistor in
the circuit.
3. The cable attaching the nodes must be daisy- chained. Drops, Taps and stubs of cables are not supported.
The addition of terminals, drops, taps, and cable stubs increase the signal reflections thus increasing the
possibility of communication errors.
4. The CABLE SHIELD is grounded at one place only. The cable shield is continuous through all nodes, but it is
isolated from the ground potential at each device.
5. The ABB protective device RS 485 ports are optically isolated, the ground wire must be attached to the shield
ground at one place only. This is required to reference the field side of the device interface to a common
reference.
RS485 Line Termination
RS 485 2 Wire connection diagrams are referenced in Figures 4 through 7. Figures 4 and 5 use the internal
resistors within the DPU, GPU, TPU and MSOC units. Figures 6 and 7 illustrate an alternate method of using
external resistors to provide biasing and line termination.
Figure 4 – RS 485 2 WIRE TERMINATION WITH THE RS 232/485 Converter INLINE and ABB
Figure 5 – Termination Using Internal Jumpers And Converter As An End Unit
One should recognize that termination is at both extreme ends of the cable. Also Figures 4 and 5 have the cable
daisy-chained, thus minimizing communication signal reflections.
TPU2000/2000R Modbus/Modbus Plus Automation Guide
Topology Diagram for RS 485 Multi-drop Architecture - if jumpers are inserted
on end units providing for proper termination.
Cable "A"
See Attached Diagram
+ 5 V
470 Ohms
Jumper J8 "IN
TX/RX +
Jumper J6 "IN" 120 Ohms
BANK SW 2
TX/RX -
Dipswitch 1 = DOWN (Term Out)
470 Ohms
Jumper J 7 "IN"
Three-wire cable with
shield. Cable "B" - See Attached Diagram.
* See Note A.
E C E C
Unit 1 Unit 2
Jumpers
End Unit Inline Unit
J6, J7, J8
"OUT"
32 Devices and 3000 Feet Maximum loading and distance.
Protective Relays At End Of Line Locations
Topology Diagram for RS 485 Multi-drop Architecture - if jumpers are inserted
on end units providing for proper termination and converter is at End Unit.
+ 5 V
470 Ohms
Jumper J8 "IN
TX/RX +
Jumper J6 "IN"
120 Ohms
TX/RX -
470 Ohms
Jumper J 7 "IN"
E C
* See Note A.
E C E C
Unit 1 Unit 2
Jumpers
End Unit Inline Unit
J6, J7, J8
"OUT"
32 Devices and 3000 Feet Maximum loading and distance.
* Note A - Following Cable Recommended
Alpha # 58902
Belden # 9729, # 9829
Carol #58902
Jumper J8 "Out"
TX/RX +
Jumper J6 "IN"
120 Ohms
TX/RX -
Jumper J 7 "Out"
E C
Unit 30 Unit 31
Inline Unit End Unit
* Note A - Following Cable Recommended
Alpha # 58902
Belden # 9729, # 9829
Carol #58902
Cable "A"
See Attached Diagram
BANK SW 2
Dipswitch 1 = IN (Term Resistor IN)
Three-wire cable with
shield. Cable "B" - See Attached Diagram.
E C
Unit 30 Unit 31
Inline Unit End Unit
E C
361