SonTek/YSI Argonaut-XR Technical Manual - HydroScientific West

A1.4. Checksum Calculation
Argonaut Operation Manual Firmware Version 7.9 (May 1, 2001)
SonTek/YSI
The Argonaut uses a checksum with each sample and whenever transmitting binary data over a
serial port. The checksum is computed with the C function "ComputeCheckSum" included
below. To understand how the checksum is computed, assume that a sample has been placed in a
segment of memory (i.e., a character array). The checksum value is stored as the last byte in this
array. The checksum is computed by the following C program statement.
CheckSum = ComputeCheckSum( buffer, Sample_Length - 1 );
In this statement, "buffer" is a pointer to the memory location where the sample begins (i.e., the
name of the character array where the sample was placed). "ComputeCheckSum" adds the first
"Sample_Length - 1" bytes starting at location buffer, then adds the value 0xA596. The result of
this summation is truncated to one (unsigned) byte and returned. The addition of the value
0xA596 is done so that an all-zeros sample does not produce a valid checksum.
#define CHECK_SUM_OFFSET 0xA596
unsigned int ComputeCheckSum( unsigned char *buf, int n )
{
int i;
unsigned int ChkSum = CHECK_SUM_OFFSET;
for(i=0;i