System information

Section 3. The CR200 Datalogger
3-9
Response packet. Calculate the signature by starting with the first byte of the
FieldName parameter and ending after the field list terminator for that table. A
description of the signature algorithm and example C code showing the method
used to calculate the signature can be found in Appendix B. Additional
examples showing functions used to parse tables from table definitions and
calculate signatures existing in the JAVA code found in Appendix D.
The table signature should be stored by the application and used in the Collect
Data Command packet when collecting data from the CR200. The datalogger
validates the table signature and ensures that the datalogger tables have not
changed when an application requests data.
Please note that table definitions and table signatures are not specifically
required if the table structure is known and the application uses the Get Values
or Set Values transaction. These transactions only require specific table
information and do not use a table signature.
3.10 Retrieving Data from the CR200
By default data are stored in ring memory on the datalogger and must be
collected by an external application before the old values are overwritten by
new values. One way an application retrieves this data is with the Collect Data
transaction. An example packet that initiates the collection process looks like:
BD A0 01 70 04 10 01 00 04 09 09 00 00 05 00 03 43 15 00 00
00 3C 00 00 C7 DF BD
The response packet from the datalogger will contain data that must be parsed.
The application uses table definition information to understand the data
structure in the packet in order to extract the appropriate information from the
response packet.
3.10.1 Interpreting Data Types
The data type determines how each value should be handled by the application.
The Appendix includes some of the data types that might be encountered when
collecting data from or sending data to a CR200.
3.10.2 Data Collection Sequence
The following steps should be used when collecting data from the CR200:
1. Get the current table definitions if necessary by using the File Upload
transaction.
2. If table definitions are returned, parse the table information from the
response packet. This information should be saved and used to interpret
collected data records. The table signature should also be calculated and
used when requesting data from the datalogger.
3. Use the Collect Data Transaction to initiate data collection from the
CR200 and parse the data contained in the Collect Data Response packet.