NOVUS AUTOMATION
1/5
DigiRail-2A
Universal Analog Input Modules
COMMUNICATION MANUAL
INTRODUCTION
The
DigiRail-2A
is provided with RS485 two wire serial communications, operating as slave in the Modbus RTU
protocol. The entire equipment configuration, as well as reading of the input data, is performed through serial
communication.
This manual provides the information necessary for reading the data from the input channels without using the software
DigiConfig
. In order to assure the correct configuration of DigiRail, always use the DigiConfig software. After being
configured, the data of its inputs and/or outputs can be accessed by any other software having Modbus RTU
communication capacity.
For further details regarding the implementation of a network of devices please refer to the document
Basic Concepts of
RS485 and RS422
, available the website
www.novusautomation.com
, for download.
MODBUS ADDRESS ASSIGNMENT SYSTEMATICS
The
DigiRail
equipment does not have keys for determination of the Modbus communication address. This must be
determined by using the communication in the Modbus protocol itself. This will require that the address of the device to
be configured is known, this being possible by two different means:
•
If the equipment is a new one, it will show the configuration as set by the factory: Address=247, Baud rate=1200,
Parity Even, 1 Stop Bit.
•
If the equipment has already been used and you do not know its address and/or other communication parameters,
press the RCom button on your front panel. It will enter the diagnostics mode during 1 minute, assuming the following
communication parameters: Address=246, Baud rate=1200, parity even, 1 stop bit.
The
DigiConfig
software configurator is provided with a function of searching the network for temporary devices, exactly
the devices in the previous conditions. Once having been localized, the address and the other communication
parameters can be changed according to the necessity of the application.
The communication parameters in the two previous conditions are not very common in Modbus networks, and they may
probably cause no conflicts with other equipment of the network. Obviously only one
DigiRail
in the network can be in
each of the previous conditions so that the communication with the configurator
DigiConfig
is possible. If several new
DigiRail
are to be included in a network, they must be inserted individually. Only after changing the communication
parameters for the definitive values, the next new
DigiRail
can be inserted. In an already existing network, only one
DigiRail
at a time can be set in diagnostics mode in order to be detected by the
DigiConfig
.
It is important to emphasize that the
DigiConfig
software acts as a master in the Modbus network. Its utilization requires
that the original master of the network (SCADA software, for instance) be disconnected during its use. For further details
please refer to the on-line Help of the
DigiConfig
.
MODBUS COMMANDS
The Modbus RTU commands (functions) listed below are implemented. For further information with respect to each one
of these commands and the Modbus protocol in general, please access the website:
http://www.modbus.org
READ INPUT REGISTERS - 04H
This command can be used for reading the current value of one or several input channels, according to the table below.
Address
Description
0
PV of Channel 1 in percentage. Range from 0 to 62000.
1
PV of Channel 2 in percentage. Range from 0 to 62000.
2 – 4
Reserved
5
PV of Channel 1 in engineering unit.
Range: defined by the limits of the temperature sensor, or by the indication limits as
defined by the parameters 42 and 43 of the
Holding Registers
.
