curtjr4 wrote:Ah, ok. I was also wondering... how can I get that "This is a test from United Video" thing working? I've been trying for quite a while... but I am having no luck.
I don't understand what you're asking? We've been able to generate our own custom titles for a while now. Can you clarify your question a bit? What are you having trouble with exactly?
nwgatwcfan wrote:I am having some trouble with setting the checksums correctly. Where are the checksums located in the data lines specifically. Do they change pending on how much data is used or what day they are set up for? I read the instructions you have provided on finding the checksums and I have them written down for use. But I wasn't sure where to go from there.
The instructions I wrote were about how to find the start byte for the checksum, not how to calculate the checksum itself. To calculate the checksum for a UVSG data message, you need to XOR the start byte with the first byte of the message you want to send. Then, you take the resulting byte, and XOR it by the next byte. Then, take that byte, and XOR it by the next byte, on and on. Include the 00 that you find at the end of a message in your checksum. The final message will look like this:
Code: Select all
55 AA <MODEBYTE> <MESSAGE> 00 <CHECKSUM>
Where modebyte is the hexadecimal equivalent of the ASCII message mode (like 50 for P, 43 for C, or 54 for T), message is the content of the message itself, 00 is always at the end of the message, and the checksum is as I described earlier. More information (albeit some of it outdated) can be found
here and
here (Note that in tin's post there is an error - he says that mode C is adverts, but it's really channels. Mode L is adverts.)
In most programming languages, an XOR is calculated with the ^ symbol, so in C, it would look something like this:
Code: Select all
int i;
int checksum = startbyte; // startbyte could be 0xAF for mode P, 0xBC for mode C, etc.
char *buffer;
for (i=0;i<strlen(buffer);i++) {
checksum = checksum ^ (int)buffer[i];
}
char *checksumString = calloc(2, sizeof *checksumString);
sprintf(checksumString, "%x", checksum);
In that code, as long as startbyte is defined and buffer is set to your message, checksumString will be the resulting checksum. If I wrote that horribly incorrectly, please someone let me know :p
Also, take a look at tin's sample perl scripts for generating messages over
here. Let me know if you still have questions, I can walk you through it a bit better over instant messaging if you need it.
Thanks to tin for figuring all of this out, of course.
