Campbell CR800 Series, Operator'S Manual, Page: 438 / 598

Section 8. Operation
438
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 CR800 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. 438)
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
addressed by default. A typical CRBasic program for a Modbus application
declares variables and ports, or variables and flags, or variables and Boolean
variables.
Modbus Registers: CRBasic Port, Flag, and Variable
Equivalents
CRBasic Port,
Flag, or Variable
Example CRBasic
Declaration
Equivalent Example
Modbus Register
C
terminal configured
for control
Public Port(4) 00001 to 00004
Flag Public Flag(17) 00001 to 00017
Boolean variable
Public ArrayB(56) as
Boolean
00001 to 00056
Variable
Public ArrayV(20)
1
40001 to 40040
1
30001 to 30040
1
1
Because of byte-number differences, each CR800 domain variable translates
to two Modbus domain input / holding registers.