About modbus, 1 outline, 2 wiring system configuration – Yokogawa RotaMASS 3-Series User Manual
Page 13: About modbus -1, 1 outline -1, 2 wiring system configuration -1
IM 01R04B08-00E-E 1st edition February 15, 2012 -00
All Rights Reserved. Copyright © 2012, Rota Yokogawa
<3. ABOUT MODBUS>
3-1
3. ABOUT MODBUS
3.1 Outline
MODBUS is a bi-directional digital communication protocol also for field devices, which offers an
advancement in communication speed and is widely employed by numerous field devices.
The MODBUS communication type of the Rotamass employs the specification standardized by the
MODBUS Organization, and provides interoperability with devices produced by other manufacturers.
Featuring transmission of all measurement variables and units as input registers and other parameters as
holding registers, the MODBUS communication type’s software enables a flexible instrumentation system to
be implemented.
For information on other features, engineering, design, construction work, startup and maintenance of
MODBUS, refer to the Modbus Organization
).
3.2 Wiring System Configuration
The number of devices that can be connected to a single bus without repeater is 32. The maximum cable
length depends on baud rate, cable properties and network configuration. When constructing systems, both
the basic and overall design must be carefully considered to allow device performance to be fully exhibited.
The following instruments are required for use with MODBUS devices:
• Terminator:
MODBUS requires two terminators at the ends of the trunk line. Refer to the supplier for details of
terminators.
• Field devices:
Connect your MODBUS communication type ROTAMASS 3 Series to a MODBUS. One or more ROTAMASS
3 Series and other field devices can be connected. For the terminal assignment on the ROTAMASS 3
Series, see chapter 4.1.
• Host:
Used for accessing field devices. A dedicated host (such as DCS) is used for an instrumentation line while
dedicated communication tools are used for startup or maintenance. For operation of the host, refer to the
instruction manual for each host. No details of the host are explained in the rest of this manual.
• Cable:
Used for connecting devices. Refer to
or
details of instrumentation cabling. If the total length of the cable is in a range of 2 to 3 meters for laboratory
or other experimental use, the following simplified cable (a twisted pair wire with a cross section of 0.9 mm²
or
more and cycle period of within 5 cm (2 inches) may be used). Termination processing depends on the type
of device being deployed. For the ROTAMASS, clamp terminal are used.
Connect the devices as shown in Figure 3.1. Connect the terminators at both ends of the trunk, with a
minimum length of the spur for connection.
The polarity of signal must be maintained.