Section 7. Installation
306
7.7.18.3 Protocols
PakBus is the protocol native to the CR3000 and transparently handles routine
point-to-point and network communications among PCs and Campbell Scientific
dataloggers. Modbus and DNP3 are industry-standard networking SCADA
protocols that optionally operate in the CR3000 with minimal user configuration.
PakBus®, Modbus, and DNP3 operate on the RS-232, CS I/O, and four COM
ports. SDI-12 is a protocol used by some smart sensors that requires minimal
configuration on the CR3000.
Read More See SDI-12 Sensor Support — Details
(p. 420),
PakBus
Comms — Overview
(p. 82),
DNP3 — Details
(p. 475),
and Modbus — Details
(p. 476).
Many instruments require non-standard protocols to communicate with the
CR3000.
Note If an instrument or sensor optionally supports SDI-12, Modbus, or
DNP3, consider using these protocols before programming a custom
protocol. These higher-level protocols are standardized among many
manufacturers and are easy to use relative to a custom protocol. SDI-12,
Modbus, and DNP3 also support addressing systems that allow
multiplexing of several sensors on a single communication port, which
makes for more efficient use of resources.
7.7.18.4 Glossary of Serial I/O Terms
Term: asynchronous
The transmission of data between a transmitting and a receiving device
occurs as a series of zeros and ones. For the data to be "read" correctly, the
receiving device must begin reading at the proper point in the series. In
asynchronous communication, this coordination is accomplished by having
each character surrounded by one or more start and stop bits which designate
the beginning and ending points of the information (see synchronous
(p. 558)
).
Indicates the sending and receiving devices are not synchronized using a
clock signal.
Term: baud rate
The rate at which data are transmitted.
Term: big endian
"Big end first." Placing the most significant integer at the beginning of a
numeric word, reading left to right. The processor in the CR3000 is MSB, or
puts the most significant integer first. See the appendix Endianness
(p. 601).
Summary of Contents for CR3000 Micrologger
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