Campbell Scientific CR7 Measurement and Control System - Manual (Page 59)

5-1
SECTION 5. TELECOMMUNICATIONS
Telecommunications allows a computer to retrieve data directly from Final Storage and may be used to
program the CR7 and monitor sensor readings in real time. Any user communication with the CR7 that
makes use of a computer or terminal instead of the CR7 keyboard is through Telecommunications.
Telecommunications can take place over a variety of links including:
• telephone
• radio frequency
• short haul modem
• SC32A and ribbon cable
• multi-drop interface and coax cable
This section does not cover the technical interface details for any of these links. Those details are
covered in Section 6 and in the individual manuals for the devices.
Data retrieval can take place in either ASCII or BINARY. The BINARY format is five times more
compact than ASCII. The shorter transmission times for binary result in lower long distance telephone
charges and more reliable data transfer. On "noisy" links shorter blocks of data are more likely to get
through without interruption.
In addition to more efficient data transfer, binary data retrieval makes use of a signature for error
detection. The signature algorithm assures a 99.998% probability that if either the data or its sequence
changes, the signature changes.
The PC208 Datalogger Support Software for PCs and compatibles contains the programs which
automate data retrieval, program transfer, and real time monitoring. The PC208 package has been
designed to meet the most common needs in datalogger support and telecommunications. This section
in not intended to furnish sufficient detail to write Telecommunications software. Appendix C contains
some details of binary data transfer and Campbell Scientific's binary data format.
This section emphasizes the commands that a person would use when manually (i.e., entered by hand)
interrogating or programming the CR7 via a computer/terminal. These commands and the responses to
them are sent in the American Standard Code for Information Interchange (ASCII). The Remote
Keyboard State (Section 5.2) allows the user with a computer/terminal to use the same commands as
the CR7 keyboard.
5.1 TELECOMMUNICATIONS
COMMANDS
When the CR7 is rung by a modem, it answers
(enables the modem) almost immediately.
Several carriage returns (CR) must be sent
from the computer to allow the CR7 to set its
baud rate to that of the modem/terminal (300,
1200, 9600, or 76,800). Once the baud rate is
set, the CR7 sends the prompt, *, signaling that
it is ready to receive a command.
GENERAL RULES governing the
telecommunications commands are:
1. * from datalogger means "ready for
command".
2. All commands are of the form: [no.]letter,
where the number may or may not be
optional.
3. Valid characters are the numbers 0-9, the
capital letters A-L, the colon (:), and the
carriage return (CR).
4. An illegal character increments a counter
and zeros the command buffer, returning *.
5. CR to datalogger means "execute".