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Section 15. Alternate Telecoms
Resource Library
15.1 Modbus
15.1.1 Overview
Modbus is a widely used SCADA communication protocol that facilitates
exchange of information and data between computers / HMI software,
instruments (RTUs) and Modbus compatible sensors. The CR200(X)
communicates via Modbus over RF and RS-232.
Modbus systems consist of a master (PC), RTU / PLC slaves, field instruments
(sensors), and the communications network hardware. The communications
port, baud rate, data bits, stop bits, and parity are set in the Modbus driver of the
master and / or the slaves. The Modbus standard has two communications
modes, RTU and ASCII. However, CR200(X)s communicate in RTU mode
exclusively.
Field instruments can be queried by the CR200(X). Because Modbus has a set
command structure, programming the CR200(X) to get data from field
instruments is much simpler than from serial sensors. Because Modbus uses a
common bus and addresses each node, field instruments are effectively
multiplexed to a CR200(X) without additional hardware.
A CR200(X) goes into sleep mode after 40 seconds of communications
inactivity. Once asleep, two packets are required before the CR200(X) will
respond. The first packet awakens the CR200(X); the second packet is received
as data.
15.1.2 Terminology
TABLE. Modbus to Campbell Scientific Equivalents
(p. 139) lists terminology
equivalents to aid in understanding how CR200(X)s fit into a SCADA system.
Table 19.
Modbus to Campbell Scientific Equivalents
Modbus Domain
Data Form
Campbell Scientific Domain
Coils Single
Bit
Ports,
Flags, Boolean Variables
Digital Registers
16-bit Word
Floating Point Variables
Input Registers
16-bit Word
Floating Point Variables
Holding Registers
16-bit Word
Floating Point Variables
RTU / PLC
CR200(X)
Master
Usually a computer
Slave
Usually a CR200(X)
Field Instrument
Sensor
Содержание CR200
Страница 32: ...Section 2 Quickstart Tutorial 22 ...
Страница 45: ...Section 3 Overview 35 3 3 Specifications ...
Страница 46: ...Section 3 Overview 36 ...
Страница 58: ...Section 4 Sensor Support 48 ...
Страница 62: ...Section 5 Measurement and Control Peripherals 52 ...
Страница 78: ...Section 8 CR200 X Configuration 68 ...
Страница 102: ...Section 9 Programming 92 ...
Страница 138: ...Section 11 Programming Resource Library 128 ...
Страница 156: ...Section 16 Support Software 146 ...
Страница 160: ...Section 17 Care and Maintenance 150 ...
Страница 166: ...Section 18 Troubleshooting 156 18 3 3 Diagnosis and Fix Procedures 18 3 3 1 Battery Voltage Test ...
Страница 167: ...Section 18 Troubleshooting 157 18 3 3 2 Charging Circuit Test Solar Panel ...
Страница 168: ...Section 18 Troubleshooting 158 18 3 3 3 Charging Circuit Test Transformer ...
Страница 169: ...Section 18 Troubleshooting 159 18 3 3 4 Adjusting Charging Circuit Voltage ...
Страница 170: ...Section 18 Troubleshooting 160 ...
Страница 184: ...Appendix A Glossary 14 ...
Страница 190: ...Appendix B Status Table and Settings 20 ...
Страница 192: ...Appendix C Serial Port Pin Outs 22 ...
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