RAD-ISM-900-EN-BD…
5-6
PHOENIX CONTACT
2476_en_I
I/O Timeout Diagnostics
In the event of a timeout, the STATUS LED flashes (at a fast two flashes per second rate)
indicating an application error. At the same time, the status LEDs on the I/O module(s) will
turn off completely when a Modbus application error exists. In addition, the radio sends an
Ethernet error message via SNMP and makes an entry into the diagnostic log web page.
When communication is re-established by the next Modbus read or write command, the
watchdog is reset, I/O communications automatically resume, an “I/O is Operational” SNMP
message is sent and a web-based diagnostic log message is entered.
Figure 5-2
Example of SNMP diagnostic error message
Duplicate I/O Addresses
Control I/O from One Source
The I/O is designed for control in a typical Modbus (RTU or TCP) master slave system. For
proper system operation, only one Modbus RTU or Modbus TCP master is allowed to
control the I/O modules. If a second Modbus master attempts to connect, the first will be
disconnected. The RAD-ISM-900-EN-BD-BUS radio allows the I/O to be controlled from
either Ethernet-based Modbus TCP or serial interface-based Modbus RTU masters. When
assigning the PLC I/O function to a communications stream, ensure that there is only one
source controlling the I/O: either a single Ethernet master source or a single serial source,
but NOT both. If two I/O control sources are assigned to the I/O stream, the error message
shown in Figure 5-3 is generated.
NOTE:
If I/O modules are installed with duplicate addresses (rotary switch settings), the I/O data
will be erroneous. When installing or changing I/O modules, ensure that the status LEDs
indicate a valid I/O configuration before reading or writing data to the I/O. Failure to do this
may result in unexpected machine or process operation.
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