Campbell Scientific PakBus Networking Guide - Manual (Page 13)

PakBus Networking Guide
neighbor added or removed, the router shares that information with other
routers on the network at a random interval.
When devices establish each other as neighbors, they must also know the port
or interface on the device they are using for communication. This port
information is included in the list of known neighbor routes. Examples of ports
that might be used for communication include RS-232, modem enable (ME),
synchronous device communications (SDC), or concurrent synchronous device
communication (CSDC).
4. PakBus Dataloggers
Datalogger with PakBus operating systems:
• Use packet-based communication
• Create specific final storage tables to logically separate different types of
data collection such as hourly, daily, rainfall, etc.
• Allow access and sharing of specific data from a table
PakBus messages are encapsulated in packets of specific size and structure.
Packets include elements such as the source and destination address for the
packet, markers declaring the type of message contained within the packet,
transaction numbers, the message or data itself, and error checking signature
nullifiers. When a packet is received, it is analyzed for errors using the
signature nullifier. If it fails the error checking process, the corrupt packet is
rejected and must be resent. Once the packet is accepted, the information
within the packet is processed and a response is generated if necessary. While
more complex, this packet structure ensures that software such as LoggerNet
can send and receive accurate commands and messages.
PakBus dataloggers allocate separate memory space for each final storage table
when the program is compiled. The datalogger knows what output tables are
required and how many fields are stored in each record at a given interval. The
datalogger partitions memory so that only the data specified in the datalogger
program are stored in the corresponding table. Each record within a table will
contain the same number of filed and along with the values in each record, a
record number and time stamp.
This table structure allows the user flexibility in terms of how much data to
store in each distinct table. The simplest scheme is to allow the datalogger to
automatically allocate table size so that all tables fill up and start overwriting
the oldest records with the newest records at the about the same time.
Alternatively, the user can create tables that contain a specified number of
records. The table structure is declared in the datalogger program.
Since data is stored a specific table with a known structure, record number, and
time stamp, the datalogger can access this data in its own table and send it to
another node or retrieve the data from the table of a different node.
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