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APPENDIX F. MODBUS ON THE CR10(X) AND CR510
Modbus communication capability is available as a Library Special on the CR10(X) and CR510
dataloggers.
The implementation of MODBUS on the CR10(X) and CR510 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 PC208.
Modbus on the CR10(X) and CR510 does not preclude interfacing with PC208 as long as the
communications system (radios, modems, etc.) is compatible with PC208.
Applications Engineers at Campbell Scientific are not proficient in, and do not provide technical support
for any of the commercially available software packages or PLCs that support Modbus. CR10(X) 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 CR10(X)s or CR510s.
F.1 TERMINOLOGY
The CR510s communicate in RTU mode (not
ASCII) to other Modbus devices.
The SCADA and MMI software packages and
Modbus use different terminology than does
Campbell Scientific. For example in SCADA
software using Modbus, to reference the
CR510's input location number 3, specify
"register 40005 F". The CR510'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 a " 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 on the CR510
correspond to coils 1, and flags 1..8 correspond
to coils 9..16.
Campbell
Scientific
input location 1,2,3...X
port 1
flag 1..8
Modbus
register 40001,40003,
40005...(40000+2X-1)
coil 1
coil 9..16
F.2 COMMUNICATIONS AND
COMPATIBILITY
Direct RS232 connect and telephone are
supported by PC208 and most SCADA software
packages. Modbus communications are on the
serial port of the CR510s. For a direct connect
to a computer an SC32A is used just as it is for
PC208 communications. Other devices such as
spread spectrum radios may require an SC932.
COM200 and VS1 telephone modems and
some radio modems are compatible with
modbus communications.
In the PC based software's Modbus driver or
with a PLC the communications port, baud rate,
data bits, stop bits, and parity are set. The
CR10(X)s communicate at 9600, 1200, or 300
baud (they automatically sync to the baud rate
of the computer), N,8,1.
The Modbus address can be set in *D mode
allowing multiple dataloggers on the same serial
port for direct communications. The address is
set in *D window 8. Valid addresses are 1 to
254 with the exception of 13.
NOTE: In earlier beta versions of the
CR510 operating system the Modbus
address is fixed at address 1.
This can be done from the CR10KD or a
computer terminal with a terminal emulator.
See section OV3 and section 5 of the CR510
manual for details.
F-1
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