8.4.1 Protocols
The CR1000 communicates with datalogger support software (p. 95) and other
Campbell Scientific dataloggers
(p. 645) using the PakBus (p. 522) protocol. See the
section Alternate Telecommunications — Details
(p. 407) for information on other
supported protocols, such as TCP/IP, Modbus, etc.
8.4.2 Conserving Bandwidth
Some telecommunication services, such as satellite networks, can be expensive to
send and receive information. Best practices for reducing expense include:
• Declare Public only those variables that need to be public.
• Be conservative with use of string variables and string variable sizes. Make
string variables as big as they need to be and no more; remember the
minimum is actually 24 bytes. Declare string variables Public and sample
string variables into data tables only as needed.
• When using GetVariables() / SendVariables() to send values between
dataloggers, put the data in an array and use one command to get the multiple
values. Using one command to get 10 values from an array and swath of 10
is much more efficient (requires only 1 transaction) than using 10 commands
to get 10 single values (requires 10 transactions).
• Set the CR1000 to be a PakBus router only as needed. When the CR1000 is a
router, and it connects to another router like LoggerNet, it exchanges routing
information with that router and, possibly (depending on your settings), with
other routers in the network.
• Set PakBus beacons and verify intervals properly. For example, there is no
need to verify routes every five minutes if communications are expected only
every 6 hours.
8.4.3 Initiating Telecommunications (Callback)
Telecommunication sessions are usually initiated by a PC. Once
telecommunication is established, the PC issues commands to send programs, set
clocks, collect data, etc. Because data retrieval is managed by the PC, several PCs
can have access to a CR1000 without disrupting the continuity of data. PakBus®
allows multiple PCs to communicate with the CR1000 simultaneously when
proper telecommunication networks are installed.
Typically, the PC initiates telecommunications with the CR1000 with datalogger
support software
(p. 654). However, some applications require the CR1000 to call
back the PC (initiate telecommunications). This feature is called 'Callback'.
Special LoggerNet
(p. 654) features enable the PC to receive calls from the CR1000.
For example, if a fruit grower wants a frost alarm, the CR1000 can contact him by
calling a PC, sending an email, text message, or page, or calling him with
synthesized-voice over telephone. Callback has been used in applications
including Ethernet, land-line telephone, digital cellular, and direct connection.
Callback with telephone is well documented in CRBasic Editor Help (search term
"callback"). For more information on other available Callback features, manuals
for various telecommunication hardware may discuss Callback options. Contact a
Campbell Scientific application engineer for the latest information in Callback
392
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