Campbell CR850 - Glossary of Terms; Table 84. Modbus to Campbell Scientific Equivalents; Terminology

Section 8. Operation
351
8.6.2.2 Terminology
Table Modbus to Campbell Scientific Equivalents (p. 351) lists terminology
equivalents to aid in understanding how CR800s fit into a SCADA system.
Table 84. 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 CR800
Master Usually a computer
Slave Usually a CR800
Field Instrument Sensor
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8.6.2.2.1 Glossary of Terms
Coils(00001to09999)
Originally,"coils"referredtorelaycoils.InCR800s,coilsareexclusively
ports,flags,oraBoolean‐variablearray.Portsareinferredifparameter
5oftheModbusSlave()instructionissetto0.Coilsareassignedto
Modbusregisters00001to09999.
DigitalRegisters10001‐19999
Holdvaluesresultingfromadigitalmeasurement.Digitalregistersinthe
Modbusdomainareread‐only.IntheCampbellScientificdomain,the
leadingdigitinModbusregistersisignored,andsoareassigned
togethertoasingleDim‐orPublic‐variablearray(read/write).
InputRegisters30001‐39999
Holdvaluesresultingfromananalogmeasurement.Inputregistersin
theModbusdomainareread‐only.IntheCampbellScientificdomain,
theleadingdigitinModbusregistersisignored,andsoareassigned
togethertoasingleDim‐orPublic‐variablearray(read/write).
HoldingRegisters40001‐49999
Holdvaluesresultingfromaprogrammingaction.Holdingregistersin
theModbusdomainareread/write.IntheCampbellScientificdomain,
theleadingdigitinModbusregistersisignored,andsoareassigned
togethertoasingleDim‐orPublic‐variablearray(read/write).