Sending 2 bytes and keeping the right order

XBee & XBee Gateway XBee - WiFi
1

Hey all.
I’ve been searching but cannot find and maybe someone could point me at the right direction: I using 2 XbeeS1 and I’m trying to send an integer from one arduino to a second one. my though was to split the int to 2 bytes but I do not know how to keep the order at which they are put together on the receiving side. Would appreciate any help/pointers.

2

The Xbee S1 will move 2 bytes anyway you send them.

Now, in AT mode, 99.9% of the time if you send them with no time gap, they will show up at the remote node as 2 bytes in the same radio packet (with no added time gap). however, in rare occasions they may move as 2 different packets.

So you may want to create a small ‘protocol’ with a header, length byte, your data and perhaps even a small CRC. Sending 5 or 6 bytes costs abotu the same as sending 2.

3

Thanks lynnl - that is what I’m trying to do but something’s not quite working - not sure why… Here are the codes - would appreciate your help:

Send:

void setup()
{ Serial.begin(38400);
 } void loop() {
 int someValue = random(0, 32767);
 outputBytes("P", someValue);
 } void outputBytes(char* header, int value){
 //translate the value into a header + 2 data bytes
 //Works for numbers upto 32767 / -32767 
//this way we know that the value is always exactly 6 bytes //makes it much easier to receive on the other end 
int MSB;
 int LSB;
 MSB = value >> 8;
 //get just the first byte 
LSB = value & 0b0000000011111111;
 //get just the second byte 
Serial.print(header);
 Serial.write(MSB);
 Serial.write(LSB);
 Serial.write(LSB);
 Serial.write(MSB);
 Serial.print(header);
 }

Receive:

void setup()
{ Serial.begin(38400)
; } void loop() { 
while(Serial.available() > 6){
 byte header = Serial.read();
 //read header byte - 80 == P
 if(header == 80){ 
byte MSB = Serial.read();
 byte LSB = Serial.read();
 byte LSB1 = Serial.read(); 
byte MSB1 = Serial.read(); 
byte foot = Serial.read();
 //make sure it fits the pattern
 if(MSB == MSB1 && LSB == LSB1 && header == foot){ 
int positionValue = convertBytes(MSB, LSB);
 Serial.print("got a value: ");
 Serial.println(positionValue);
 }
else
{ Serial.println("that didnt work");
 Serial.print("MSB: ");
 Serial.println(MSB);
 Serial.print("LSB: ");
 Serial.println(LSB);
 Serial.print("LSB1: "); 
Serial.println(LSB1);
 Serial.print("MSB1: ");
 Serial.println(MSB1);
 Serial.print("foot: ");
 Serial.println(foot);
 Serial.println("/////////////////"); }
 }
else
{
 Serial.print("HEADER WAS NOT A P");
 Serial.print("header: ");
 Serial.println(header);
 Serial.println("/////////////////");
 } } }
 int convertBytes(int MSB, int LSB){
 //99% sure this is right 
return(MSB << 8) | LSB;
 //get just the first byte 
} void doMotorThing(int positionValue)
{
 //do something with the positionValue
 }