Campbell Scientific CR3000 Micrologger - Manual (Page 373)

Section 8. Operation
373
Table 91. 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 CR3000
Master Usually a computer
Slave Usually a CR3000
Field Instrument Sensor
8.6.2.2.1 Glossary of Terms
Coils (00001 to 09999)
Originally, "coils" referred to relay coils. In CR3000s, 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).
RTU / PLC
Remote Telemetry Units (RTUs) and Programmable Logic Controllers
(PLCs) were at one time used in exclusive applications. As technology
increases, however, the distinction between RTUs and PLCs becomes
more blurred. A CR3000 fits both RTU and PLC definitions.