4. Configuration
69
Simultaneous
requests per
instance
Simultaneous
requests per
device
Table 4-26. MODBUS Protocol Limitations for Symbolic Mappings
Notes:
Devices per instance:
ï‚· Master or Client Protocol: Number of slave or server devices supported by each Master or
Client protocol instance.
ï‚· Slave MODBUS RTU Protocol: the limit (1) informed relates to serial interfaces that do not
allow a Slave to establish communication through the same serial interface, simultaneously, with
more than one Master device. It’s not necessary, nor is it possible to declare or configure the
Master device in the instance of the MODBUS RTU slave protocol. The master device will have
access to all the mappings made directly on the instance of MODBUS RTU slave protocol.
ï‚· MODBUS RTU Server Protocol: the limit
(2)
informed relates to the Ethernet interfaces, which
limit the amount of connections that can be established with other devices through a single
Ethernet interface. It is not necessary, nor is it possible to declare or configure Clients devices in
the instance of the MODBUS Server protocol. All Clients devices will have access to all the
mappings made directly in the instance of the MODBUS Server protocol.
Requests by device: Number of requests, such as reading or writing holding registers, that can be
configured for each of the devices (slaves or servers) from Master or Client protocols instances. This
parameter does not apply to instances of Slave or Server protocols.
Simultaneous Requests per Instance: Number of requests that can be simultaneously transmitted
by each client protocol instance or that can be received simultaneously by each server protocol
instance. MODBUS RTU protocol instances, Master or Slave, do not support simultaneous requests.
Simultaneous Requests per Device: Number of requests that can be simultaneously transmitted for
each MODBUS server device, or may be received simultaneously from each MODBUS client
device. MODBUS RTU devices, Master or Slave do not support simultaneous requests.
ATTENTION:
Simultaneous requests to a variable associated to communication points, those which support the
SBO operation mode (Select Before Operate), even being received from differente devices are not
supported. Once started the selection/operation of a point by a specific device, that must be finished
before this point become able to be commanded by another device.
ATTENTION:
MODBUS communication drivers for symbolic mappings are available only from 1.3.0.20 version
of Nexto Series CPUs. Similarly to use this feature is required MasterTool IEC XE version 1.40 or
later.
The protocol Server IEC 60870-5-104 limitations can be watched on Table 4-27.
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