I-1
Appendix I. Modbus on the CR10 and
CR10X
Modbus communication capability is available as a Library Special on the CR10 and CR10X
dataloggers.
The implementation of MODBUS on the CR10 and CR10X allows input locations, ports, and
flags to be read or to be set. Not supported are historical data retrieval, program downloads,
setting the clock, and other functions of PC208W/PC208.
Modbus on the CR10 and CR10X does not preclude interfacing with PC208W or PC208 as
long as the communications system (radios, modems, etc.) is compatible.
Applications Engineers at Campbell Scientific do not provide technical support for any of the
commercially available software packages or PLCs that support Modbus. CR10 users have
successfully communicated using the following software packages: Wonderware Intouch,
Labview, Iconics Genesis for DOS, and Citect for Windows. LabTech’s modbus driver does
not support floating point, and thus is not compatible with the CR10 range.
I.1 Terminology
The CR10/10X communicates in RTU mode (not ASCII) to other Modbus
devices.
SCADA, MMI software packages and Modbus use different terminology from
Campbell Scientific. For example, in SCADA, running software using Modbus, to
reference the CR10/10X’s input location number 3, specify ‘register 40005 F’.
The CR10/10X’s input locations are analogous to registers in Modbus. Because of
floating point considerations, two registers of memory are required for each input
location. Modbus registers are offset by 40000, therefore the register equivalent of
any input location X is: 40000+2X-1. The register is followed by an ‘ F’ in the
Intouch software. Ports and flags are more straight forward. Modbus does not
differentiate between ports and flags. They have ‘coils’, originally meaning coil
relays that are either on or off. Ports 1..8 on the CR10 correspond to coils 1..8, and
flags 1..8 correspond to coils 9..16.
Campbell
Scientific
Modbus
input location 1,2,3...X
register 40001,40003, 40005...(40000+2X-1)
port 1..8
coil 1..8
flag 1..8
coil 9..16
I.2 Communications and Compatibility
Direct RS232 connection and telephone communication are supported by
PC208W/PC208 and most SCADA software packages. Modbus communications
are on the serial port of the CR10/10Xs. For a direct connect to a computer an
SC32A is used just as it is for PC208W/PC208 communications. Other devices
such as spread spectrum radios may require an SC932. DC112 telephone modems
and some radio modems are compatible with modbus communications.