User Manual

9-1
C H A P T E R 9
Modbus
Many newer SCADA and process control systems connect either
directly or wirelessly to measurement devices through a serial
connection or wireless modem to q uickly access p r o cess values.
One of the industry standard protocols through which this occurs i s
Modbus. Th e ADS
®
TRITON+
™
monitor serves as a Mo dbus slave
device and provides process values based on Modbus holding
registers through an ExPAC inter face o r wirelessl y thr ough 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. I t specifically addresses the Modb us data registers.
For Modbus wireless data exchange, refer to Chapter
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 b e
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, may be used in
place of an RTU. ADS
®
references the RTU in this
manual prima rily because it is the most common type of
end-point hardware use d with SCADA systems.