Campbell Scientific CR510 CR510 Basic Datalogger - Page 193
Appendix F., Modbus On The Cr10x And Cr510
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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 Modbus input location 1,2,3...X port 1 flag 1..8 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