Campbell Scientific CR1000KD CR800 and CR850 Measurement and Control Systems - Page 352

Section 8. Operation 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. 8.6.2.3 Programming for Modbus 8.6.2.3.1 Declarations Table CRBasic Ports, Flags, Variables, and Modbus Registers (p. 352) shows the linkage between CR800 ports, flags and Boolean variables and Modbus registers. Modbus does not distinguish between CR800 ports, flags, or Boolean variables. By declaring only ports, or flags, or Boolean variables, the declared feature is addressed by default. A typical CRBasic program for a Modbus application will declare variables and ports, or variables and flags, or variables and Boolean variables. Table 85. CRBasic Ports, Flags, Variables, and, Modbus Registers CR800 Feature Example CRBasic Declaration Equivalent Example Modbus Register Control Port (Port) Public Port(8) 00001 to 00009 Flag Boolean Variable Variable Public Flag(17) Public ArrayB(56) as Boolean Public ArrayV(20)* 00001 to 00018 00001 to 00057 40001 to 40041* or 30001 to 30041* *Because of byte-number differences, each CR800 domain variable translates to two Modbus domain input / holding registers. 8.6.2.3.2 CRBasic Instructions - Modbus Complete descriptions and options of commands are available in CRBasic Editor Help. ModbusMaster() Sets up a CR800 as a Modbus master to send or retrieve data from a Modbus slave. Syntax ModbusMaster(ResultCode, ComPort, BaudRate, ModbusAddr, Function, Variable, Start, Length, Tries, TimeOut) ModbusSlave() Sets up a CR800 as a Modbus slave device. Syntax ModbusSlave(ComPort, BaudRate, ModbusAddr, DataVariable, BooleanVariable) MoveBytes() Moves binary bytes of data into a different memory location when translating big‐endian to little‐endian data. 352