Bus Configuration for I/O Modules (RAD-ISM-900-EN-BD-BUS only)
2476_en_I
PHOENIX CONTACT
5-3
5
Bus Configuration for I/O Modules
(RAD-ISM-900-EN-BD-BUS only)
5.1
RAD I/O Communications
5.1.1
Modbus TCP I/O Emulation Operation
Modbus TCP data is sent into the radio configured as the Modbus Gateway. The data is
directed to a specific TCP port number (502 for Modbus). This data is then converted to
Modbus RTU protocol and sent to all other radios in the network on one of the two available
serial streams. At the remote radios, the Modbus packets are sent to the I/O ports (RS-232,
RS-485/422 or the I/O modules) that are assigned to that serial stream.
If the serial stream is assigned to I/O modules on a RAD-ISM-900-EN-BD-BUS and the
Modbus node address of the radio matches that in the packet, a standard Modbus RTU
response packet will be generated. The analog I/O values are stored in the 4xxxx registers,
the digital input values are stored in the 1xxxx series registers, and the digital outputs are
controlled by writing to the 0xxxx registers. The 8-position rotary switch on the top of each
I/O module determines the register where each module's I/O will be located (see Table 5-1
and Table 5-2).
When a Modbus RTU response packet is received at the master radio, the radio converts
the Modbus RTU packet back into a Modbus TCP packet and sends the data through the
Ethernet port to the host device.
5.1.2
System Overview
The RAD-ISM-900-EN-BD-BUS radio allows up to eight RAD I/O modules to be controlled
by a Modbus (RTU or TCP) based PLC/PC (or other Modbus master device). The group of
RAD I/O modules, connected to a RAD-ISM-900-EN-BD-BUS radio, act as a single Modbus
slave I/O station, and communicate over a wired or wireless serial communications stream
to a Modbus TCP or Modbus RTU master PLC (or other type of controlling device).
Typical I/O Applications
Many application configurations are possible including the following:
1.
A master PLC connected to any RAD-ISM-900-EN-BD-BUS radio and configured as
either a master or slave. Configured as wireless, the master PLC controls RAD I/O
attached to remotely mounted RAD-ISM-900-EN-BD-BUS radios in slave mode.
a)
Master PLC connects to the radio's serial port and uses Modbus RTU.
b)
Master PLC connects to the radio's Ethernet port and uses Modbus TCP.
2.
A master PLC connected to a RAD-ISM-900-EN-BD-BUS radio and configured as a
master. The master PLC controls both locally attached RAD I/O and controls I/O
attached to remotely mounted RAD-ISM-900-EN-BD-BUS radios in slave mode.
–
Master PLC connects to the radio’s serial port and uses Modbus RTU
–
Master PLC connects to the radio’s Ethernet port and uses Modbus TCP
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