Serial.readBytes()

Descrição

Serial.readBytes() lê caracteres da porta serial e os move para um buffer. A função termina se a quantidade de bytes determinada foi lida, ou se ocorre time-out (ver Serial.setTimeout()).

Serial.readBytes() retorna o número de caracteres colocados no buffer. Um valor 0 indica que dados não foram encontrados.

A função Serial.readBytes() é herdada da classe Stream.

Sintaxe

Serial.readBytes(buffer, length)

Parâmetros

  • Serial: objeto porta serial. Veja a lista de portas seriais disponíveis em cada placa no Serial - Página principal
  • buffer: o buffer para se armazenar os bytes (char[] ou byte[])
  • length : o número de bytes a serem lidos (int)

Retorna

o número de bytes colocados no buffer (size_t)

Código de Exemplo

const int BUFFER_SIZE = 50; char buf[BUFFER_SIZE]; void setup() { Serial.begin(9600); // opens serial port, sets data rate to 9600 bps } void loop() { // check if data is available if (Serial.available() > 0) { // read the incoming bytes: int rlen = Serial.readBytes(buf, BUFFER_SIZE); // prints the received data Serial.print("I received: "); for(int i = 0; i < rlen; i++) Serial.print(buf[i]); } }
  • Type "HELLO" on Serial Monitor and click Send button:
  • COM6
    Send
    Autoscroll Show timestamp
    Clear output
    9600 baud  
    Newline  
  • The result on Serial Monitor:
  • COM6
    Send
    I received: HELLO
    Autoscroll Show timestamp
    Clear output
    9600 baud  
    Newline  

※ Notas e Advertências:

  • Serial.readBytes() may read a stream of bytes in multiple times (resulting in multiple fragments). To read a stream of bytes at one time, there are two ways:
    • Based on the delimiter: Use Serial.readBytesUntil() with delimiter.
    • Based on the fixed length: Wait until the fixed number of bytes is available. for example:
const int BUFFER_SIZE = 5; char buf[BUFFER_SIZE]; void setup() { Serial.begin(9600); // opens serial port, sets data rate to 9600 bps } void loop() { // check if data is available if (Serial.available() >= BUFFER_SIZE) { // read the incoming bytes: Serial.readBytes(buf, BUFFER_SIZE); // TODO: PROCESS THE INCOMING DATA HERE } }
  • Make sure that the read length does NOT exceed the buffer size. The below is the best practice:
const int BUFFER_SIZE = 5; char buf[BUFFER_SIZE]; // application buffer void setup() { Serial.begin(9600); // opens serial port, sets data rate to 9600 bps } void loop() { // check if data is available int rxlen = Serial.available(); // number of bytes available in Serial buffer if (rxlen > 0) { int rlen; // number of bytes to read if (rxlen > BUFFER_SIZE) // check if the data exceeds the buffer size rlen = BUFFER_SIZE; // if yes, read BUFFER_SIZE bytes. The remaining will be read in the next time else rlen = rxlen; // read the incoming bytes: rlen = Serial.readBytes(buf, rlen); // TODO: PROCESS THE INCOMING DATA HERE } }
  • Serial functions are not only used for the communication between an Arduino board and Serial Monitor of Arduino IDE but also used for the communication between:
    • An Arduino board and other Arduino board
    • An Arduino board and other sensors/devices
    • An Arduino board and computer (any Serial software on computer)

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