Campbell CR800 Series - Glossary of Serial I;O Terms; Protocols

Section 7. Installation
281
CR800 Serial Ports
Serial Port Voltage Level Logic
RS-232 (9 pin) RS-232
Full-duplex asynchronous RS-
232
CS I/O (9 pin) TTL
Full-duplex asynchronous RS-
232
COM1 (C1 – C2) TTL
Full-duplex asynchronous RS-
232/TTL
COM2 (C3 – C4) TTL
Full-duplex asynchronous RS-
232/TTL
C1
5 VDC SDI-12
C3
5 VDC SDI-12
C1, C2, C3
5 VDC
SDM (used with Campbell
Scientific peripherals only)
7.7.17.3 Protocols
PakBus is the protocol native to the CR800 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 CR800 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 CR800.
Read More See SDI-12 Sensor Support — Details
(p. 385), PakBus
Comms — Overview (p. 77), DNP3 — Details (p. 436), and Modbus — Details
(p. 436).
Many instruments require non-standard protocols to communicate with the
CR800.
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.
7.7.17.4 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