CODEWITHSUNDEEP
microchipusart
j.valerio
j.valerio

Reputation: 11

dsPic Receive 11byte usart string

I'm using a dsPic33 to try and receive a 11-byte string and place it in a array, but have not been successful at receiving it completely. The string I send is "$123456789#" which should be received by the pic. I have tried using the code below. Any help will be appreciated.

char inBytes[11];
int i;
unsigned char temp;

while (U1STAbits.URXDA != 0)
{
  temp = U1RXREG;
  if (temp == '$')
  {
      inBytes[0] = temp;
      for(i = 1; i < 10; i++)
      {
        if (U1STAbits.URXDA != 0)
        inChar = U1RXREG;
        inBytes[i] = inChar;
      }
  }

Upvotes: 0

Views: 1418

Answers (2)

Mathieu L.
Mathieu L.

Reputation: 438

jolati had a good point about the end value beeing too low to get 11 bytes but I must add that you have to wait for your other bytes to become available before you read them.

In your example;

char inBytes[11];
int i;
unsigned char temp;

while (!U1STAbits.URXDA ); //Wait until at least one byte is available

temp = U1RXREG;
if (temp == '$')
{
    inBytes[0] = temp;

    for(i = 1; i < 11; i++) //Loop over range i = 1 to 10 inclusively
    {
        while (!U1STAbits.URXDA ); //Wait until at least one byte is available
        inBytes[i] = U1RXREG;
    }
}

Ideally, you would do this in a non blocking way with interrupts so you handle your data as it comes in but, if you cant use interrupts, you can always use non blocking polling like:

void AsyncRX()
{
    //Note that the static variables keeps their value between invocations of the
    //  function. i is set to 0 only on the first run of this function, it keeps 
    //  its value on every other run after that.
    static int i = 0;
    static char inBytes[11];

    //Nothing more to do until there is at least 1 byte available
    if( !U1STAbits.URXDA ) 
        return;

    //Save the byte and test that our message starts with $
    inBytes[i] = U1RXREG;
    if( inBytes[0] != '$' )
        return;

    //Test the counter to see if we have a full 11 bytes
    i++;
    if( i < 11 )
        return;

    //Do something with your 11 bytes
    //...
    //...

    //Reset the counter for the next message
    i = 0;
}

For the interrupt example, you could simply grab the polled version and throw it into a ISR. The following is an example. Note that I do not know which dsp33 you are using and I have not programmed interrupts in high end cores (with vector tables) in a while so you may need to make a change or two. Also note that you need to enable interupts by setting the appropriate registers as they are not enabled by default.

void __attribute__ ((interrupt, no_auto_psv)) _U1RXInterrupt(void) 
{
    //Note that the static variables keeps their value between invocations of the
    //  function. i is set to 0 only on the first run of this function, it keeps 
    //  its value on every other run after that.
    static int i = 0;
    static char inBytes[11];

    //Reset the interrupt flag
    IFS0bits.U1RXIF = 0;

    //Use up all bytes in the buffer (the interrupt can be set to only fire 
    //  once the buffer has multiple bytes in it).
    while( U1STAbits.URXDA ) 
    {
        //Save the byte and test that our message starts with $
        inBytes[i] = U1RXREG;
        if( inBytes[0] != '$' )
            continue;

        //Test the counter to see if we have a full 11 bytes
        i++;
        if( i < 11 )
            continue;

        //Do something with your 11 bytes
        //...
        //...

        //Reset the counter for the next message
        i = 0;
    }
}

Upvotes: 1

jolati
jolati

Reputation: 700

for(i = 1; i < 10; i++) starts saving data at index 1 and stops at 9, only 9 bytes. Change < 10 to <= 10 or < 11.

Upvotes: 1

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