Modbus Communications - Campbell CR300 Series Product Manual

protocol and then select the appropriate options for each CRBasic parameter. See the application
note Interfacing Serial Sensors with Campbell Scientific Dataloggers
details and examples.
NOTE:
Though Com1 (C1/C2) uses RS-232 logic levels, it is limited to 0 V (logic high) and 5 V (logic
low) output. This may make Com1 incompatible with some serial devices.
Com1 is not capable of TTL logic levels and so is not compatible with TTL-to-RS-232
converters for the purpose of presenting a true RS-232 interface.
Com1 also has a low input resistance that may make it incompatible with some serial devices
with the addition of in-line resistance.

15.2 Modbus communications

The data logger supports Modbus RTU, Modbus ASCII, and Modbus TCP protocols and can be
programmed as a Modbus master or Modbus slave. These protocols are often used in SCADA
networks. Data loggers can communicate using Modbus on all available communication ports.
The data logger communicates using Modbus over RS-232 using a RS-232-to RS-485 adapter and
over TCP using an Ethernet or Wireless connection.
CRBasic Modbus instructions include:
ModbusMaster()
l
ModbusSlave()
l
MoveBytes()
l
See the CRBasic Editor help for detailed instruction information and program examples:
https://help.campbellsci.com/crbasic/cr300/.
For additional information on Modbus, see:
About Modbus
l
Why Modbus Matters: An Introduction
l
How to Access Live Measurement Data Using Modbus
l
Using Campbell Scientific Dataloggers as Modbus Slave Devices in a SCADA Network
l
Because Modbus has a set command structure, programming the data logger to get data from
field instruments can be much simpler than from some other serial sensors. Because Modbus uses
a common bus and addresses each node, field instruments are effectively multiplexed to a data
logger without additional hardware.
(p. 88)
for more programming
15. Communications protocols 87