Operator`s manual

5-1
SECTION 5. TELECOMMUNICATIONS
Telecommunications allows a computer to retrieve data directly from Final Storage and may be
used to program the 21X and monitor sensor readings in real time. Any user communication with
the 21X that makes use of a computer or terminal instead of the 21X 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 program
TELCOM which automates data retrieval and TERM which will upload and download programs
and monitor Input Storage. 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 21X 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 21X keyboard.
5.1 TELECOMMUNICATIONS
COMMANDS
When the 21X 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 21X to set its baud
rate to that of the modem/terminal (300, 1200,
9600, or 76,800). Once the baud rate is set, the
21X 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 *.