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How to set and use SYNCHRONOUS USART using C-PIC compiler?

 
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Judy_Perri
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How to set and use SYNCHRONOUS USART using C-PIC compiler?
PostPosted: Thu Mar 18, 2004 11:53 am     Reply with quote

I am using the PCW C compiler to compile my C code for PIC628A on which there is an USART. I would like to use it in SYNCHRONOUS mode. How should I set this up and use the interupt to receive data? Can I use the builtin function for RS232? If not how should I do it? Thanks in advance.
Charlie U



Joined: 09 Sep 2003
Posts: 183
Location: Somewhere under water in the Great Lakes

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PostPosted: Thu Mar 18, 2004 6:17 pm     Reply with quote

Here's some bits and pieces to get you started:

Code:

// Interrupt flags
#bit TXIF = 0x0C.4
#bit RCIF = 0x0C.5

#bit RX9D = 0x18.0
#bit OERR = 0x18.1
#bit FERR = 0x18.2
#bit ADEN = 0x18.3
#bit CREN = 0x18.4
#bit SREN = 0x18.5
#bit RX9  = 0x18.6
#bit SPEN = 0x18.7

#bit TX9D = 0x98.0
#bit TRMT = 0x98.1
#bit BRGH = 0x98.2
// bit 0x98.3 is undefined in 16F627
#bit SYNC = 0x98.4
#bit TXEN = 0x98.5
#bit TX9  = 0x98.6
#bit CSRC = 0x98.7

// Interrupt enables
#bit TXIE = 0x8C.4
#bit RCIE = 0x8C.5

#byte TXREG = 0x19
#byte RCREG = 0x1A
#byte SPBRG = 0x99

void put_serial(int tx_data)
{
   while(!TXIF)
   {
      restart_wdt();
   }
   TXREG = tx_data;
   return;
}

int get_serial()
{
   while(!RCIF)
   {
      restart_wdt();
   }
   return RCREG;
}

void TransmitData(void)
{
   int j = 0;
   SYNC = TRUE;
   CREN = FALSE;
   CSRC = TRUE;
   do
   {
      put_serial(TransmitBuffer.Data[j++]);  // Send the data then increment j
   } while ((TransmitBuffer.Data[j-1] != 0x0D) && (j < BUFFERLENGTH));
}

main() // extracted from main
{
      // set comm to sync master transmit
      SPBRG = 0x19;
      SYNC = TRUE;
      CREN = FALSE;
      SPEN = TRUE;
      CSRC = TRUE;
      TXEN = TRUE;
      // Construct a message and send
   
   your code goes here

     TransmitData();
      // wait for transmit to complete
      // then loop for multiple commands
      // first wait for the transmit interrupt flag (TXREG is empty)
      while (1)
      {
         while (!TXIF)
         {
            restart_wdt();
         }
         // then wait for the TSR register to empty
         while (!TRMT)
         {
            restart_wdt();
         }
         // set comm to sync slave receive
         SYNC = TRUE;
         CSRC = FALSE;
         CREN = TRUE;
         ReceiveBuffer.Index = 0;
         do
         {
            // Wait for data to be received
            while (!RCIF)
            {
               restart_wdt();
            }
            receiveddata = get_serial();
            _other code_
         } while ((receiveddata != 0x0D) &&
               (Index < BufferLength));
}


The above is NOT fully functional, it is just the main stuff you would need to get started with sync serial setup. The original program ping-ponged messages back and forth, switching between master and slave.

You could set this up with true interrupts, but for my application, it was just waiting for a message, then did something based on the message received.

Hope this helps.
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