EPRAD eCNA-10 - Event Log Summary: Event Flags Explained

© EPRAD Incorporated
6.18 Checksum
A checksum is appended to the end of all messages to help detect errors in transmission. The
checksum is an unsigned 16-bit decimal sum of all characters preceding the checksum. The
checksum is obtained by adding all the decimal values of ASCII characters that make up a command
or response. Logically ‘AND’ 65535 to this sum or repeatedly subtract 65536 (2
16
) from this sum until
the remainder is less than 65536 to get the final 16-bit decimal checksum value.
Checksum Calculation Example:
Command Response
CMD,RID,0,[ ]<CR><LF> RSP,RID,0,0,eCNA-10,1010,1,[ ]<CR><LF>
The Command is: The Response is:
Command
Character
ASCII
Value
Response
Character
ASCII
Value
C 67 R 82
M 77 S 83
D 68 P 80
, 44 , 44
R 82 R 82
I 73 I 73
D 68 D 68
, 44 , 44
0 48 0 48
, 44 , 44
615 0 48
, 44
The checksum is 615 and the complete command is: e 101
C 67
CMD,RID,0,615<CR><LF> N 78
A 65
- 45
1 49
0 48
, 44
1 49
0 48
1 49
0 48
, 44
1 49
, 44
1568
The checksum is 1568 and the complete response is:
RSP,RID,0,0,eCNA-10,1010,1,1568<CR><LF>
If ?? is added to the instruction instead of a checksum, the instruction is executed. It sends a “don’t
care” value for the checksum. This method is not recommended for programming because it does not
insure proper communication error checking.
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eCNA-10 Operation and Installation Manual Version 1.270-00