Teledyne 2103Ci, Installation And Operation Manual, Page: 33 / 74

3-1
2103 Modem Module
Section 3 Modbus Protocol
Sections 3.1 through 3.5 give an overview of the basic capabilities
and operation of Modbus protocol as it applies to Isco 2100 Series
flow modules.
For a Glossary of Terms and Common Acronyms, see sections 3.4
and 3.5.
For Modbus technical specifications, turn to section 3.6.
3.1 Introduction
Modbus is a simple command/response mechanism to read from
and write to specific memory locations called
registers . A register
is a holding place for a piece of digital information within the
equipment. There are three standard protocols for Modbus:
Modbus RTU, Modbus TCP/IP, and Modbus ASCII. The Isco 2100
Series devices use Modbus ASCII protocol, the method discussed
in this manual. Modbus ASCII has more liberal communication
timing requirements. Modbus communication for the Isco 2100
Series provides a standard protocol that can be used to retrieve
real-time data from a single module or stack of modules at a site,
or multiple sites, over a wide area. The data can be sent to a
central computer for display, data collection, or process control.
Modbus implementation is independent of Flowlink and cannot
alter the Flowlink-programmed configuration of the module.
Modbus cannot be used to retrieve historical data from a
module’s memory.
Due to the wide variety of configurations that can be made with
Modbus, it is impossible to cover every usable application. This
section will discuss the overall capabilities and operation of
Modbus.
3.2 Operation
There are many standard, third party Modbus drivers and OPC
servers that may be used to link a remote Modbus device, such as
a 2100 Series module, to SCADA or process control software,
such as Wonderware™ or Intellution™. The OPC server commu-
nicates with the remote instrumentation and accesses registers.
The definition of what information is contained and where (the
register number, or address) is decided by the manufacturer
(Teledyne Isco).
In a 2100 module, the registers hold, but are not limited to, the
current real-time value of the meter’s level, velocity, flow, input
voltage, temperature, and total flow readings, stored in specified
register locations. A list of the 2100 register addresses, and what
parameters are held where, is available in section 3.6.