Campbell CR3000 Micrologger, Operator'S Manual

Page: 477 / 644

Section 8. Operation
477
8.10.3.1.1 Glossary of Modbus Terms
Term: coils (00001 to 09999)
Originally, "coils" referred to relay coils. In CR3000s, coils are exclusively
terminals configured for control, software flags, or a Boolean-variable array.
Terminal configured for control are inferred if parameter 5 of the
ModbusSlave() instruction is set to 0. Coils are assigned to Modbus
registers 00001 to 09999.
Term: digital registers 10001 to 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).
Term: input registers 30001 to 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).
Term: holding registers 40001 to 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).
Term: 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.
8.10.3.2 Programming for Modbus
8.10.3.2.1 Declarations (Modbus Programming)
Table Modbus Registers: CRBasic Port, Flag, and Variable Equivalents
(p. 478)
shows the linkage between terminals configured for control, flags and Boolean
variables and Modbus registers. Modbus does not distinguish between terminals
configured for control, flags, or Boolean variables. By declaring only terminals
configured for control, or flags, or Boolean variables, the declared feature is