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302 Modbus Communication
Upgrading a Mark II to a Mark III Reference, Installation, and Operations Manual
June 2013 3-9000-743 Rev S
C.3 Modbus Communication
C.3.1 Protocols
The Mark III meter supports ASCII and RTU Modbus communication. For ASCII Modbus, both
7E1 and 7O1 are supported. For RTU Modbus, 8N1 is supported. The communication ports
provide automatic protocol detection - only the baud rate and Modbus ID need to be specified.
Refer to Section 5.1 for details on configuring the meter communication parameters.
C.3.2 Registers
The Mark III uses a database for managing its information in which each piece of information is
stored in a database point. The meter utilizes a mapping file for cross-referencing database
points with Modbus registers for Modbus data access. Refer to Section 6.4 for further details.
The Mark III maintains backward compatibility to Mark II Modbus registers whenever possible.
The UnitsSystem register selects the units for Modbus communications. Available options are
U.S. Customary and Metric. These are the units in which the software Field Setup Wizard
displays properties. These are also the units with which the meter reports all of its rates and
volumes using Modbus communications. The selected units system applies only to registers
above 10000 and in the 2000-8999 range, other registers below 10000 are read in metric units
only to maintain Mark II compatibility. US customary units is the default setting.
For Modbus access information for a particular data point, consult
Daniel MeterLink online help. (There is a help topic for each data point. From Daniel MeterLink,
click on Help, click on Mark III Registers Reference, select the Index tab, start typing the data
point name until the desired point is highlighted, and then click the Display button.)
The Modbus map is available in Microsoft Excel format (MARK III Modbus Table.xls) on the Daniel
MeterLink CD and the Daniel website http://www2.emersonprocess.com/en-US/brands/daniel/
Flow/ultrasonics/Pages/Ultrasonic.aspx). Note that on the website, the file name may include
the file size (MARK III Modbus Table 386KB.xls).
The Daniel MeterLink program includes a means of converting a Mark II meter configuration to a
Mark III meter configuration for use in upgrading electronics heads. This feature is discussed in
Section C.4 below.
C.3.3 Log Access
Due to the Mark III meter’s enhanced log retrieval methods, accessing log records via Modbus
communication is not supported. All log records (daily, hourly, audit, alarm, and system) are
optionally accessible via Daniel MeterLink (see Section 6.6.6).