ABB TPU2000, Technical Manual, Page: 371 / 374

TPU2000/2000R Modbus/Modbus Plus Automation Guide
361
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.
Cable “A”
See Attached Diagram
E C E C E C
32 Devices and 3000 Feet Maximum loading and distance.
E C
Unit 1 Unit 2 Unit 30 Unit 31
Three-wire cable with
shield. Cable “B” - See Attached Diagram.
End Unit Inline Unit Inline Unit End Unit
Jumpers
J6, J7, J8
“OUT”
+ 5 V
120 Ohms
470 Ohms
470 Ohms
Jumper J8 “IN
Jumper J 7 “IN”
Jumper J6 “IN”
TX/RX +
TX/RX -
Topology Diagram for RS 485 Multi-drop Architecture - if jumpers are inserted
on end units providing for proper termination.
* See Note A.
* Note A - Following Cable Recommended
Alpha # 58902
Belden # 9729, # 9829
Carol #58902
120 Ohms
Jumper J8 “Out”
Jumper J6 “IN”
TX/RX +
TX/RX -
Jumper J 7 “Out”
T
E
LE
B
Y
T
E
245
RS
232/ RS
422/485
BANK SW 2
Dipswitch 1 = DOWN (Term Out)
Figure 4 – RS 485 2 WIRE TERMINATION WITH THE RS 232/485 Converter INLINE and ABB
Protective Relays At End Of Line Locations
Cable “A”
See Attached Diagram
E C E C
E C
32 Devices and 3000 Feet Maximum loading and distance.
E C
Unit 1 Unit 2 Unit 30 Unit 31
Three-wire cable with
shield. Cable “B” - See Attached Diagram.
End Unit Inline Unit Inline Unit End Unit
Jumpers
J6, J7, J8
“OUT”
+ 5 V
120 Ohms
470 Ohms
470 Ohms
Jumper J8 “IN
Jumper J 7 “IN”
Jumper J6 “IN”
TX/RX +
TX/RX -
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.
* See Note A.
* Note A - Following Cable Recommended
Alpha # 58902
Belden # 9729, # 9829
Carol #58902
TE
LE
B
Y
T
E
245
R
S
23
2/
R
S
422/
48
5
BANK SW 2
Dipswitch 1 = IN (Term Resistor IN)
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.