How to read an array of bytes through Serial.read(

Forum 2005-2010 (read only) Software Bugs & Suggestions
#1

Hi,

I am new to arduino.I am trying to communicate two arduino modules using Xbee modules. From one arduino am sending an array of 9 bytes, wih syntax:

Serial.write(RFout,9); //RFout is an array with 9 bytes

On the other hand, the other arduino trying to recieve this information by using the below syntax:

int availableBytes = Serial.available();
delay(2000);
if (Serial.available() > 0) {

for(int n=0; n<availableBytes; n++);
{
RFin_bytes[n] = Serial.read();
}

But, it seems to be not working.Could you people help me out in solving this problem.

#2

Doesn’t available() just return the number of bytes available now, which might only be 1. You need an outer loop to keep trying to read till all the 9 bytes have been acquired? Something like:

  int bytes_read = 0 ;
  while (bytes_read < 9)
  {
     if (Serial.available() > 0)
     {
        ...... read a byte and store it ....
        bytes_read ++;
     }
  }

Or you could wait for available() to return at least 9 before reading all 9 - the hardware buffer is 128 bytes.

#3

I've just noticed your code is buggy anyway as you assume the two calls to available() return the same value, which is not guaranteed.

#4

Sorry, i didn't understand the second reply. So could you please help me in storing the 9 bytes of incoming string.

#5 
int availableBytes = Serial.available();
delay(2000);

Two seconds is a very long time to wait. If your serial line is running constantly at 9600 baud, the serial receiver buffer would overflow in less than a fifth of a second.

#6

Why make it so complicated?
How about:

while (Serial.available()<9) {} // Wait 'till there are 9 Bytes waiting
for(int n=0; n<9; n++)
   RFin_bytes[n] = Serial.read(); // Then: Get them.
#7

One thing always to keep in mind when writing this kind of code is to be able to handle things when something goes wrong – like what if you never get the 9 bytes you are expecting? I doubt you would want your code to lock up.

I’d probably do something like this:

#define MAX_MILLIS_TO_WAIT 1000  //or whatever
unsigned long starttime;

starttime = millis();

while ( (Serial.available()<9) && ((millis() - starttime) < MAX_MILLIS_TO_WAIT) )
{      
      // hang in this loop until we either get 9 bytes of data or 1 second
      // has gone by
}
if(Serial.available() < 9)
{
            // the data didn't come in - handle that problem here
      Serial.println("ERROR - Didn't get 9 bytes of data!");
}
else
{
      for(int n=0; n<9; n++)
         RFin_bytes[n] = Serial.read(); // Then: Get them. 
}
#8

Don't forget to flush the buffer on error. ;)

#9