10-1
C H A P T E R 10
Modbus
Many newer SCADA and process control systems connect either
directly or wirelessly to measurement devices through a serial
connection or wireless modem to quickly access process values.
One of the industry standard protocols through which this occurs is
Modbus. The ADS TRITON+
®
monitor serves as a Modbus slave
device and provides process values based on Modbus holding
registers through an ExPAC interface (using a customer-supplied
cable) or wirelessly through the internal cellular modem.
This chapter contains essential connection and reference
information regarding communication and data exchange through a
serial connection involving the TRITON+, ExPAC/XBUS, and
RTU. It also addresses Modbus wireless data exchange and
Modbus data registers.
Note: An RTU (remote terminal unit) is an example of
the kind of customer-supplied equipment that uses
Modbus acquired data. Many other types of equipment
may be connected to TRITON+ monitors; however, all
will communicate as described. A PLC (programmable
logic controller), an I/O (input/output) server, or other
instruments, such as the Telog
®
Ru-33 or Ru-35, may be
used in place of an RTU. ADS
®
references the RTU in this
manual primarily because it is the most common type of
end-point hardware used with SCADA systems.
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