How do I send a payload to an XBee - embedded

Question

I have implemented the following code on an embedded platform that attempts to communicate with an XBee. The embedded platform that executes the code below is not an xbee:
int main()
{
char payload[12] = {0x61,0x88,0x00,0x64,0x00,0x00,0x00,0x00,0x00,0xEC,0x00,0x00}
payload[2] = 0x10;
payload[9] = 0x01;
char data = 'H'; // Send simple ASCII character to XBee
payload[11]= data;
while (1)
sendByteofData(payload,12);
}
void sendByteOfData(char * payload, int len)
{
int x;
for (x=0;x<4;x++)
// This function sends IEEE 802.15.4 frames, and I know it
// works because they are detected in the [sniffer][3].
send_IEEE_802_15_4_frame(payload,len);
}
payload[2] = payload[2] % 256 + 1;
payload[9] = payload[9] % 256 + 1;
if (payload[9] % 256 == 0 )
payload[9] = 0x01;
else
payload[9] %= 256;
}
To my surprise the above code actually sent one byte from the embedded platform to the XBee successfully. however, the infinite loop at the end of main() should have produced a stream of bytes.
My suspicion is I need to set payload[2] and payload[9] correctly, and there is probably a flaw in the incremental modulo 256 algorithm shown above.
How do I get a continuous stream of bytes?

Answer 1

A few thoughts...
Make your payload an array of unsigned char or, even better, uint8_t.
To update payload[2] and payload[9], simplify your code:
++payload[2];
++payload[9];
if (payload[9] == 0) payload[9] = 1;
Add a delay between sends. You might even need to wait for a response before sending the next character.
Since it's a payload of unsigned 8-bit values, they'll automatically roll from 255 to 0. I assume your special case code for payload[9] is trying to roll from 255 to 1 (instead of 0).
Make sure your payload doesn't need to include a checksum of some sort. Updating those two bytes would have an affect on a checksum byte.