Campbell Scientific CR23X Micrologger - Manual (Page 272)

APPENDIX C. BINARY TELECOMMUNICATIONS
C-4
As an example of a positive value, the
datalogger returns 44 D9 99 9A HEX.
Data byte 1 = 44 HEX.
Data byte 2 to 4 = D9 99 9A HEX (or 891290
decimal).
Data byte 1 is converted to binary to find the
Sign. 44 HEX = 01000100 BINARY.
NOTE: Don’t lose the leading zero!
The most significant bit is 0 so the Sign is
POSITIVE.
The exponent is found by subtracting 40 HEX
from the remaining least significant bits.
Converting the binary to hexadecimal, 1000100
BINARY = 44 HEX (or 68 decimal).
44 - 40 HEX = 4 HEX. Or in decimal:
68 - 64 = 4.
Exponent is 4 decimal.
The binary equivalent of Data bytes 2 to 4 is:
11011001 10011001 10011010.
Summing all the fractional values:
2
-1
+ 2
-2
+ 2
-4
+ 2
-5
+ 2
-8
+ 2
-9
+ 2
-12
+ 2
-13
+ 2
-16
+
2
-17
+ 2
-20
+ 2
-21
+ 2
-23
= 0.85000.
Using the estimate method to find the Mantissa =
D9 99 9A HEX / 1 00 00 00 HEX (or 14260634 /
16777216) which is 0.85000 decimal.
The value is then (+)0.85*2
4
which equals
13.60.
If appropriately requested by a J command,
Final Storage data, if any, will immediately
follow the input location data. Refer to the
datalogger manual for a description of how to
decode Final Storage data in CSI's binary data
format. Final Storage data will be limited to not
more than 1024 bytes per K command.
The K command data is terminated with 7F 00
HEX (a unique binary format code) followed by
two signature bytes. Refer to the datalogger
manual for the meaning and calculation of the
signature bytes. The signature in this case is a
function of the first time byte through the 7F 00
HEX bytes. Calculate the signature of the bytes
received and compare with the signature received
to determine the validity of the transmission.
C.2 FINAL STORAGE FORMAT
CR23X data is formatted as either 2 byte LO
Resolution or 4 byte HI Resolution values. The
first two bytes of an Output Array contain a unique
code (FC Hex) noting the start of the Output Array
and the Output Array ID, followed by the 2 or 4
byte data values. At the end of the data sent in
response to the telecommunications F command a
2 byte signature is sent (see below).
Representing the bits in the first byte of each
two byte pair as ABCD EFGH (A is the most
significant bit, MSB), the byte pairs are
described here.
LO RESOLUTION FORMAT - D,E,F,
NOT ALL ONES
Bits Description
A Polarity, 0 = +, 1 = -.
B, C Decimal locators as defined below.
D-H plus 13 bit binary value (D=MSB).
second Largest possible number without D,
E, and F all 1 is 7167,
byte but CSI defines the largest
allowable range as 6999.
The decimal locators can be viewed as a
negative base 10 exponent with decimal
locations as follows:
B C Decimal Location
0 0 XXXX.
0 1 XXX.X
1 0 XX.XX
1 1 X.XXX
DATA TYPE WHEN D,E,F, ALL EQUAL ONE
If D, E, and F are all ones, the data type is
determined by the other bits as shown below. X
implies a "don't care" condition; i.e., the bit can
be either 1 or 0 and is not used in the decode
decision.