5. CONFIGURATION
Configuration Description Default Value Options
Read Filter Mask
Specifies the subnet mask in
conjunction with the IP filter
parameter for reading.
0.0.0.0
0.0.0.0 to
255.255.255.255
Table 125: IP Filters
Note:
Filters: filters are used to establish a range of IP addresses that have write or read access to MODBUS relations, being
individually configured. The permission criteria is accomplished through a logical AND operation between the Write Filter
Mask and the IP address of the client. If the result is the same as the Write Filter IP Address, the client is entitled to write. For
example, if the Write Filter IP Address = 192.168.15.0 and the Write Filter Mask = 255.255.255.0, then only customers with
IP address = 192.168.15.x shall be entitled. The same procedure is applied in the Read Filter parameters to define the read
rights.
In the previously defined relations, the maximum MODBUS data size can be 65536 (maximum value configured in the
Data Size field). However, the request which arrives in the MODBUS Ethernet Server must address a subgroup of this mapping
and this group must have, at most, the data size depending on the function code which is defined below:
Read Coils (FC 1): 2000
Read Input Status (FC 2): 2000
Read Holding Registers (FC 3): 125
Read Input Registers (FC 4): 125
Write Single Coil (FC 5): 1
Write Single Holding register (FC 6): 1
Force Multiple Coils (FC 15): 1968
Write Holding Registers (FC 16): 123
Mask Write Register (FC 22): 1
Read/Write Holding Registers (FC 23):
• Read: 121
• Write: 121
ATTENTION
Differently from other application tasks, when a depuration mark in the MainTask is reached,
the task of an Ethernet MODBUS Server instance and any other MODBUS task will stop
running at the moment that it tries to perform a writing in a memory area. It occurs in order
to keep the consistency of the memory areas data while a MainTask is not running.
5.5.10. OPC DA Server
It’s possible to communicate with the Nexto Series CPUs using the OPC DA (Open Platform Communications Data
Access) technology. This open communication platform was developed to be the standard in industrial communications.
Based on client/server architecture, it offers several advantages in project development and communication with automation
systems.
A very common analogy to describe the OPC DA technology is of a printer. When correctly connected, the computer needs
a driver to interface with the equipment. Similarly, the OPC helps with the interface between the supervision system and the
field data on the PLC.
When it comes to project development, to configure the communication and exchange information between the systems is
extremely simple using OPC DA technology. Using other drivers, based on addresses, it’s necessary to create tables to relate
tags from the supervision system with variables from the programmable controller. When the data areas are changed during
the project, it’s necessary to remap the variables and create new tables with the relations between the information on the PLC
with the Supervisory Control And Data Acquisition system (SCADA).
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