MODBUS Interface
Verbatim Owner's Manual F-15
F.12 RC Linking/Network Bridging
The commands detailed in this section allow data to be passed between any two
remote channels. Applications include passing data between nodes on
compatible and incompatible networks, updating status registers in DCS
systems, or exporting the Verbatim physical I/O to remote nodes. One channel
acts as a data “source” and the second as a data “destination”. Data is read from
the source channel’s net address and then written to the destination channel’s
net address once per scan loop. The destination and source are said to be
“linked”.
F.12.1 Linking Modes
The linking functions can work in one of two modes. In Data Link mode, the
data read from the source is written directly to the destination. In the absence of
communication problems, each destination channel is updated with a frequency
equal to the Verbatim scan time. If there is a communications problem reading
data from the source, then nothing is written to the destination.
In Alarm Link mode, the source channel data is first interpreted against the
configured alarm criteria. If any alarm condition exists at the SRC channel,
then a 1 is written to the DST. Otherwise, 0 is written. Any communications
problem reading from the source will be reflected.
For both modes, the reads and writes are attempted once per scan loop. Any
required protocol conversions are handled automatically. Any problems getting
data for or writing data to the destination will appear as communications errors
on the source or destination RCs. The data read or written is subject to RC
initialization and the worst-case scan loop latencies. See Section F.7 for details.
F.12.2 Commands & Limitations
The commands below establish the channel linkage configurations. There are
several rules and restrictions as follows:
1. Both the source and destination RCs must already be configured with net
addresses. If this is not the case, then an error message is given. The net
address for either channel in a linked pair may be reconfigured at any
time, without altering the link.
2. If the RC specified as source is already configured as destination for any
other linked pair, then an error message is given. Similarly, if the RC
specified as destination is already configured as source for any other
linked pair, an error message is given. This prevents “chaining” of linked
pairs.
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