ABB REX 521 Technical Reference Manual, General

38
1MRS 751108-MUM
Protection Relay
Technical Reference Manual, General
REX 521
At physical level, the Modbus systems may use different physical interfaces, for
example, RS-485 or RS-232 (see Figure 4.1.12.8.-1). Both the RS-485 two-wire
interface and the optical RS-232 interface are supported by REX 521. The
recommended RS-485 bus topology with Modbus is a chain of devices with line
terminations at the both ends of the bus.
Fig. 4.1.12.8.-1 Example of a Modbus system
The adjustable parameters via HMI for Modbus communication in REX 521 are
CRC Order, Modbus Mode, Unit Address, Baud rate, No of stop
bits, No of data bits, End of frame TO, and Parity.
When using the RTU mode, every time the bit rate parameter (the Baud
rate) is reconfigured (value is changed) the software of REX 521 also
recalculates the default value for timeout parameter (End of frame
TO). Therefore, to manually enforce the timeout value, the timeout
parameter must always be set after configuring the Baud rate
parameter. In this case it is recommended to set the parameter value for
longer timeout than the calculated default value with the Baud rate
parameter in question.
For more information of Modbus, see Modbus Remote Communication Protocol for
REX 521, Technical Description (see “Related documents” on page 7).
Modbus Master
C
E
F
I
0
REF 54_ relays
REX 521
REX52x REX52x
REX5 2x
RER 133
RS232 RS485
RS485 INTERFACE
12345678
4 WIRE TERMINATED
S1
OFFON ONOFF OFF NC NC NC
S2 ON ON ON ON ON ON NC NC
4 WIRE WITHOUT TERMINATION
S1
OFFON ONOFF OFF NC NC NC
S2 OFFOFFOFF OFF OFF OFF NC NC
2 WIRE TERMINATED
S1
ONOFF ON OFFOFF NC NC NC
S2 OFFOFFOFF ON ON ON NC NC
2 WIRE WITHOUT TERMINATION
S1
ONOFF ON OFFOFF NC NC NC
S2 OFFOFFOFF OFF OFF OFF NC NC
S1
S2
ON
ON
OFF
OFF
2WIRE
8A +
7B 
6A +
5B 
4AGND
3NC
2 Shield GND C
1 Shield GND
4WIRE
RX
TX

RER133_front_a
C
E
F
I
0
RER 133
RS232 RS485
RS485 INTERFACE
12345678
4 WIRE TERMINATED
S1
OFFON ONOFF OFF NC NC NC
S2 ON ON ON ON ON ON NC NC
4 WIRE WITHOUT TERMINATION
S1
OFFON ONOFF OFF NC NC NC
S2 OFFOFFOFF OFF OFF OFF NC NC
2 WIRE TERMINATED
S1
ONOFF ON OFFOFF NC NC NC
S2 OFFOFFOFF ON ON ON NC NC
2 WIRE WITHOUT TERMINATION
S1
ONOFF ON OFFOFF NC NC NC
S2 OFFOFFOFF OFF OFF OFF NC NC
S1
S2
ON
ON
OFF
OFF
2WIRE
8A +
7 B 
6A +
5 B 
4AGND
3NC
2 Shield GND C
1 Shield GND
4WIRE
RX
TX

RER133_front_a
C
E
F
I
0
RER 133
RS232 RS485
RS485 INTERFACE
12345678
4 WIRE TERMINATED
S1
OFFON ONOFF OFF NC NC NC
S2 ON ON ON ON ON ON NC NC
4 WIRE WITHOUT TERMINATION
S1
OFFON ONOFF OFF NC NC NC
S2 OFFOFFOFFOFF OFFOFF NC NC
2 WIRE TERMINATED
S1
ONOFF ON OFFOFF NC NC NC
S2 OFFOFFOFF ON ON ON NC NC
2 WIRE WITHOUT TERMINATION
S1
ONOFF ON OFFOFF NC NC NC
S2 OFFOFFOFFOFF OFFOFF NC NC
S1
S2
ON
ON
OFF
OFF
2WIRE
8A +
7 B 
6A +
5 B 
4 AGND
3NC
2 Shield GND C
1 Shield GND
4WIRE
RX
TX

RER133_front_a
RS-485 twisted pair
Modbus_sys_REXREF_a
RER 133
RER 133
RER 133
!

ABB REX 521 Specifications

General

Brand	ABB
Model	REX 521
Category	Other
Language	English