Modbus; Modbus Related Interface; Bus Topology; Connection To Modbus - IMP PUMPS NMT Max C Installation And Operating Manual

7. MODBUS

7.1. MODBUS RELATED INTERFACE

Designation
MODE
LED2 / ACT
B/D-
A/D+
COM/0V

7.2. BUS TOPOLOGY

NMTC is a Modbus slave, connected directly to a Modbus RTU network. Connection can be made in either
daisy chain style (if cabling allows such a connection) or a limited length passive tap. Schematic example is in
Figure 6.
Slave 1
Typically, only one master device is connected to the serial bus, and one or several slaves are also
connected to the bus. Slaves do not communicate with each other and will never transmit data
without receiving a proper request from the master device.
Up to 32 single load devices can be connected to one RS-485 Modbus
system without using a repeater. As this module is a 1/8 load device, up to 256 modules can be
connected to the bus. Repeaters can be used to extend the maximum
transmission distance and increase device count if needed.

7.3. CONNECTION TO MODBUS

A screened, twisted-pair cable should be used. The cable screen must be connected to the COM
terminal and connected to safety ground at one point.

7.4. SPEED, PARITY AND ADDRESS

By default, each device is set to 19200-E-1 (even parity), address 245.
Properly set registers in section "7.7 NMTC Configuration register block" to configure each device before
connecting it to existing network. Optionally power each device one by one, configuring the settings before
adding another one.
There are several ways to restore forgotten Modbus connection settings:
1) Configure the module over Web interface. See section 6 "Ethernet".
2) Reset the module to factory defaults. See Mode 9, section "4.3 Module mode selection".
3) If only address is unknown, Modbus "broadcast" (0x00) address can be used to write new address.
Use carefully as the value will be written to all connected devices.

7.5. TERMINATION

NMTC module contains neither termination nor bias circuitry. RS-485 wiring should be externally terminated if
needed.
Description
Can be used to reset network configuration
Indicates Ethernet activity or Modbus reception.
RS-485 negative data signal for Modbus.
RS-485 positive data signal for Modbus.
RS-485 common and analog input common (ground).
Master
Passive tap
Figure 6: Example of Modbus network
Slave 2 Slave 3
Daisy chain
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