ABB UMC100.3 Manual - Página 4

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U N I V E R S A L M OTO R C O N T R O L L E R U M C 1 0 0 . 3 | M R P 3 1 . 0 M O D B U S T C P C O M M U N I C AT I O N M O D U L E M A N U A L

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Overview

This chapter contains a short description of the RS-485 standard and the MRP31.0 Modbus Interface module.

RS485 Standard

RS-485 is a serial interface standard for communication over a twisted-pair cable. Because the RS-485 signal transmission is

differential, it provides better protection against noise and longer transmission distances than the RS-232. RS-485 is a

half-duplex multi-drop network, which means that multiple devices may reside on line. Only one transmitter may be active at

any given time. The RS-485 standard specifies only the electrical characteristics of the bus system.

The RS-485 transmission line consists of two wires, A and B. The signal transmission is based on the voltage difference

between the wires. The potential difference between the two wires determines the logic state bit: when B is at higher

voltage than A, the state is defined as bit 1 (data high) and when A is at higher voltage than B, the state is defined as bit 0

(data low).

Ground wire and cable shield should be connected to prevent common mode voltage between the network devices from

drifting outside the allowable limits. RS-485 bus cable should be terminated with a 120 Ohm resistor on both ends to

prevent signal reflection.

The MRP31.0 Modbus Interface

The MRP31.0 Modbus communication interface is an optional device for the UMC100.3 which enables the connection of the

UMC100.3 to a RS-485 network. The MRP31.0 provides galvanic isolation between the UMC100.3 and the RS-485 network.

• Use operator panel UMC100-PAN on UMC100.3 to set bus address, baud rate and timeout of the Modbus communication.

Parity and frame length are automatically detected

• MRP31.0 supports the RTU transmission mode only

• MRP31.0 is considered as a slave on the Modbus RTU network. Only one master can communicate with the MRP31.0 at a

time.

Through the interface you can:

• Give control commands to the UMC100.3 (for example Start, Stop, Fault Reset)

• Read status information and actual process values from the UMC100.3

• Read device diagnosis information

MRP31

Top View

Status Indication

LEDs

X3:

Modbus

connection

X3: Modbus connection

X2: 24V DC

X1: Communication

supply connection

to UMC100.3

Side View