Campbell Scientific CR10 CR10 Measurement and Control - Page 214

APPENDIX C. BINARY TELECOMMUNICATIONS CSI defines the largest allowable range of a high resolution number to be 99999. Interpretation of the decimal locator for a 4 byte data value is given below. The decimal equivalent of bits GH is the negative exponent to the base 10. BITS GHA 000 001 010 011 100 101 DECIMAL FORMAT 5 diqits XXXXX. XXXX.X XXX.XX XX.XXX X.XXXX .XXXXX C.3 GENERATION OF SIGNATURE At the end of a binary transmission, a signature is sent. The signature is a 2 byte integer value which is a function of the data and the sequence of data in the Output Array. lt is derived with an algorithm that assures a 99.998% probability of detecting a change in the data or its sequence. The CRl O calculates the signature using each transmitted byte beginning with the Final Storage format data (for K command, echo and carriage return line feed are not included) untilthe 2 byte signature itself. By calculating the signature of the received data and comparing it to the transmitted signature, it can be determined whether the data was received correctly. SIGNATURE ALGORITHM o 31,S0 - represent the high and low bytes of the signatu re, respectively o M - represents a transmitted data byte . n - represents the existing byte o n+1 - represents the new byte o T - represents atemporary location o C - represents the carry bit from a shift operation 1. The signature is initialized with both bytes set to hexadecimalAA. 51(n)=Ss(n)=AA 2. When a transmitted byte, M(n+1), is received, form a new highsignature byte by setting it equalto the existing low byte. Save the old high byte for later use. Tr = Sr(n) 51(n+1) = So(n) 3. Form a temporary byte by shifting the old low signature byte one bit to the left and adding any carry bit which results from the shift operation. A "shift left" is identicalto a multiply by 2. lgnore any carry bit resulting from the add. Tz = shift left (Ss(n)) + carry 4. Form the new low signature byte by adding the results of operation 3 to the old high signature byte and the transmitted byte. lgnore any carry bits resulting from these add operations. S6(n+1) =T2+ 51(n) + M(n+l) As each new transmitted byte is received, the procedure is repeated. c-4