MODBUS Interface
F-8 Verbatim Owner's Manual
F.6 PLC Address Format
The table below shows how to address specific objects in Modicon PLCs. ‘x’
represents a digit in the range 0-9. The Verbatim autodialer User Interface will
accept any values for ‘xxxx’. If a value is out of range for a particular PLC, that
PLC will issue an error diagnostic, which will be passed on to the user. This is
to say, the remote PLCs enforce the validity of PLC addresses on their own.
Notes:
K Extended memory access is not currently implemented.
K Inputs may be written by the Verbatim autodialer, but will most likely be
overwritten immediately by the PLC when it does its next scan of the
ladder logic.
K The PLC memory protect switch will prevent a coil or register from being
written.
Addressing Modicon PLC Objects
Address Description
0xxxx Coil (1-bit Output) number xxxx
1xxxx Input point (1-bit) number xxxx
3xxxx Input register (16-bit) number xxxx
4xxxx Output (holding) register (16-bit) number xxxx
F.7 Potential Effects of Network
Communications Failures
Physical channels only go into alarm state when their input matches
programmed alarm criteria. Remote channels also support these criteria-based
alarms.
It must be remembered however, that the channel data compared against the
criteria must first be received from the network being monitored. Since the
remote channel’s data is being transferred over a network, alarming may be
affected by various network failures.
If such a failure occurs, and the data cannot be received, it is no longer possible
to reliably compare the channel against the alarm criteria. As a result, the
remote channels will enter the alarm state even though their channel data may
not have changed. The term “COMALARM” is used to distinguish this sort of
alarm scenario from the criteria based alarms.
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