incoming data buffered?

Projects Programming
1

Hi!

I'm having troubles with serial communication and I'm not sure if I understood the concept of receiving bytes well so I would need some clarification.

Does the Serial receive have some kind of buffer where it stores incoming bytes until my software reads them, or do I risk losing bytes if they happen to arrive when my program is busy doing something else? I always assumed the received bytes sit there waiting until my program reads them out. Is this correct?

If this is the case, when I will read the bytes out later, which byte comes out first? The most recently received byte or the oldests?
I mean, say I would send 'ABC' to the Arduino's serial port and say a moment later I would do IncomingByte = Serial.read(), would it return the 'A' or the 'C'?

Thanks a lot!

2

Yes, the UART has a buffer. Can't remember how long though.

3

would it return the 'A' or the 'C'?

A. The buffer is "first in, first out" (FIFO)

Hope that helps..

4

The HardwareSerial object has a buffer and how long it is depends on the version of software and the amount of RAM in use, but is usually 64 or 128 bytes.

5

hello
I also have one question
I'm trying to receive a message from a gsm modem but I think I have a buffer problem.
If I connect the modem using a hiperterminal client I received all the message ok, connecting it to arduino mega I just can retrieve half of the message.Coult it be because buffer overflow??
were is my code

//Read new SMS from Motorola C168i to Arduino and print to LED panels
//Program developed by Matthew Mosher ©2010


#include <NewSoftSerial.h>

NewSoftSerial modem_gsm(10, 11);
char sms[500];
int i;


void setup()  
{
  Serial.begin(9600);
  Serial.println("Goodnight moon!");

  // set the data rate for the NewSoftSerial port
  modem_gsm.begin(9600);
  delay(500);
  modem_gsm.println("AT+CMGF=0\r\n");  // Set modem_gsm mode to text (vs pdu)
  delay(500);
  modem_gsm.flush();
  delay(300);


}



void loop()                     // run over and over again
{


  modem_gsm.print("AT+CMGR=1"); 

  modem_gsm.println("\r\n"); 
  delay(500);

  // Debug Loop
  for (i = 0; i < 500; i++) {
  if (modem_gsm.available() > 0) {
      char c = modem_gsm.read();
     Serial.print(c, BYTE);
      }
    delay(10);   
  }
  

  delay(300);
  modem_gsm.flush();
  delay(300);

}


}

this is what I should expect like in hiperterminal:
+CMGR: 1,,22
0791539126010000040C915391862668620000212080013203000331D90C

OK

And this is what arduino reply when connect to the modem:

AT+CMGR=1

+CMGR: 1,,22
0791539126010000040C91539186266862000

The rest of the message is missing.Another thing that is bugging me is why it apears "AT+CMGR=1" on the output since I'm just seending it to the modem, it should not expected to see it when receiving!!!
any help

6

What is the point of the for() loop? You only check serial available 500 times. Why would you expect the message to be completed by then?

7

yes you are right.can you sugest a simple way to just received what is in the buffer? thanks

8

Problem solved:
using the softserial library aparently the buffer is lower.Since arduino board have 3 UART ports i remove the library and use the serial1 and it works now.