Campbell Scientific CR10 CR10 Measurement and Control - Page 72

SECTION 5. TELECOMMUNICATIONS 4. An illegal character increments a counter and zeros the command buffer, returning a *. 5. CR to datalogger means "execute". 6. 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 aboft the command sequence with CRLF* and to zero the command buffer. 8. Allcommands return a response code, usually at least a checksum 9. The checksum includes allcharacters sent by the datalogger since the last *, including the echoed command sequence, excluding only the checksum itself. The checksum is formed by summing the ASCIlvalues, without parity, of the transmitted characters. The largest possible checksum value is 8191 . Each time 8191 is exceeded, the CR10 starts the count over; e.9., 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 CR10 sends ASCII data with 8 bits, no parity;one start bit, and one stop bit. After the CR10 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. lt "hangs up" if it does not receive a valid character in this time i Some modems are quite noisy when not on it is possible for valid characters to appear in the'noise pattern. To insure that this situation does not keep the CR10 in the CR10 counts allthe invalid characters it receives from the time it answers a ring, and terminates communication after receiving 150 invalid characters. The CR10 continues to execute its measurement and processing tasks while servicing the telecommunication requests. lf the processing overhead is large (short Execution lnterval), the processing tasks will slow the telecommunication functions. In a worst case situation, the CR10 interrupts the processing tasks to transmit a data point every 0.125 second. The best way to become familiar with the Telecommunication Commands is to try them from a terminalconnected to the CR10 via the SC32A (Section 6.7.1) or other interface. Commands used to interrogate the CR10 in the Telecommunications Mode are described in the following Table. 5-2