I am working on a node integration to a home automation device. The device
has an ASCII protocol that I am building a parser and a command generator
for.
All of the ASCII messages that I send need to be appended with modulo 256
checksum. Here is the exact verbiage from the documentation.
2-digit checksum: This is the hexadecimal two’s complement of the
> modulo-256 sum of the ASCII values of all characters in the message
> excluding the checksum itself and the CR-LF terminator at the end of the
> message. Permissible characters are ASCII 0-9 and upper case A-F. When all
> the characters are added to the Checksum, the value should equal 0.
>
I have an ASCII string of *09sw13100* that is supposed to result in hex *B8.
*That is what I am using as my test.
Any ideas on how to implement this? I've tried the function below but it
produces the wrong output.
function calcChecksum(asciiString) {
var buf = new Buffer(asciiString);
var sum = 0;
for(var i=0; i<buf.length; i++) {
sum = sum + buf[i];
}
sum = sum%256;
return sum.toString(16);
}
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