Campbell SkyVUE 8, Product Manual

Page: 74 / 116

6. Messages
6.1 Data messages general 62
6.2 Checksums used in SkyVUE 8 messages 62
6.3 CS messages 63
6.4 CL31 messages 76
6.5 CT25K messages 85
6.1 Data messages general
The SkyVUE 8 can provide a variety of data message types to allow efficient output of data. Not
all messages provide the full information available, but these messages may be more efficient in
terms of data storage and transmission.
CL31 and CT25K messages follow formats used by common existing CL31 and CT25K sensors
allowing easier replacement or network expansion.
6.2 Checksums used in SkyVUE 8 messages
This is based on the CRC-16 with the output XOR’d with Hex 0xFFFF and outputs a two-byte
CRC-16 character. The CRC-16 is calculated on all characters after the SOH character up to and
including the ETX character.
The following example uses the
C
code to calculate the SkyVUE 8 checksum.
NOTE:
Shorts are 16 bits long and ints are 32 bits long.
// ----------------------------------------------------------------
// Calculate CRC-16
// buf is a pointer to the input string
// len is the length of the input string
// ----------------------------------------------------------------
unsigned short crc16(char *buffer, int length)
{
unsigned short crc;
unsigned short m;
int i, j;
crc = 0xFFFF;
for (i=0; i < length; ++i)
{
SkyVUE™8 (CS136) LIDAR Ceilometer 62