Campbell Scientific CR23X Micrologger - Manual (Page 74)

SECTION 5. TELECOMMUNICATIONS
5-2
GENERAL RULES governing the
telecommunications commands are as follows:
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-U, the colon (:), and the
carriage return (CR).
4. An illegal character increments a counter
and zeros the command buffer, returning a
∗∗∗∗
.
5. CR to datalogger means "execute".
6. A carriage return followed immediately by a
line feed character (CRLF) from datalogger
means "executing command".
7. ANY character besides a CR sent to the
datalogger with a legal command in its buffer
causes the datalogger to abort the command
sequence with CRLF
∗∗∗∗
and to zero the
command buffer.
8. All commands return a response code,
usually at least a checksum.
9. The checksum includes all characters sent by
the datalogger since the last
∗∗∗∗
, including the
echoed command sequence, excluding only
the checksum itself. The checksum is
formed by summing the ASCII values, without
parity, of the transmitted characters. The
largest possible checksum value is 8191.
Each time 8191 is exceeded, the CR23X
starts the count over; e.g., if the sum of the
ASCII values is 8192, the checksum is 0.
10. Commands that return Campbell Scientific
binary format data (i.e., F and K
commands) return a signature (see
Appendix C.3).
The CR23X sends ASCII data with 8 bits, no
parity, one start bit, and one stop bit.
After the CR23X answers a ring, or completes a
command, it waits about 40 seconds (127
seconds in the Remote Keyboard State) for a
valid character to arrive. It "hangs up" if it does
not receive a valid character in this time interval.
Some modems are quite noisy when not on line;
it is possible for valid characters to appear in
the noise pattern. To insure that this situation
does not keep the CR23X in
telecommunications, the CR23X counts all the
invalid characters it receives from the time it
answers a ring, and terminates communication
after receiving 150 invalid characters.
The CR23X continues to execute its
measurement and processing tasks while
servicing the telecommunication requests. If
the processing overhead is large (short
Execution Interval), the processing tasks will
slow the telecommunication functions. In a
worst case situation, the CR23X interrupts the
processing tasks to transmit a data point every
0.1 second.
The best way to become familiar with the
Telecommunication Commands is to try them
from a terminal connected to the CR23X via the
SC32A (Section 6.7.1) or other interface.
Commands used to interrogate the CR23X in
the Telecommunications Mode are described in
the following Table.