PIC 18f1220 EUSART Baud Rate Cache Problem

[wklose99]

I'm in the middle of a project I've been working on for about the last 3 weeks.

What I have is an ID-12 RFID reader(https://www.sparkfun.com/commerce/product_info.php?products_id=8419) to read passive RFID tags. The reader outputs at 9600 baud. However, I need to send the data output from the ID-12 reader through a wireless RF transmitter(https://www.sparkfun.com/commerce/product_info.php?products_id=7816) which takes in data at a max of 4800 baud. I am using the built in USART Rx/Tx pins on a PIC 18F1220 to accomplish this cache job. What I am having trouble programming in MPLAB using C language is a routine for setting the baud rate to 9600, receiving all the bits, then changing the baud to 4800, and sending the bits.

I thought we had the send/receive part down in the code and were just using improper SPBRG values, however it turns out we were using the correct SPBRG values but our code was faulty. I know our SPBRG values work properly and our clock source is alright because we wrote tests for the pic which worked both at 9600 baud and 4800 baud. Our old cache code was faulty mainly due to the interrupts that were being used. So we have given up on the interrupt driven USART and have decided to just do a polled while loop. Since all we need the PIC18f1220 for is caching this ID-12 output we decided interrupts are not essential. We spent hours combing through the datasheet and setting values manually but decided to use the usart.h library functions instead. Below is the
code we are trying to get working, however for some reason it is not. If someone would take a look at it and suggest what we are doing wrong I would be very appreciative.

Thanks much, -WK


Specs on project:
PIC: 18f1220
Compiler: C18 C-language compiler used in MPLAB
Computer OS: Windows XP


Code:

//*
 * The following application is a cache program for converting a 9600 baud RFID card reader output
 * to 4800 baud so it can be fed into a RFID transmitter input. The clock is 8Mhz, BRGH is 1, and BRG16 is 0.
 * The PIC used is an 18f1220.
 * The progam is compiled in C using the MC18 compiler on a Windows XP laptop.
 */
#include <p18f1220.h>
#include <usart.h>


#pragma config OSC = HS	 //external crystal clocked at 8Mhz
#pragma config WDT = OFF	
#pragma config LVP = OFF

void main (void)
{
	unsigned char c;            //grab the transmitted char in here
	unsigned char myCache[16];	//we will cache the input in here
	unsigned int counter=0;     //This keeps track of which byte were on
	int j = 0;

	//The next 5 initializations are set according to the PIC datasheet
	//requirements for USART recieve/trans

	TRISBbits.TRISB1 = 1;	//TX set to output
	TRISBbits.TRISB4 = 1;   //RX set to 1, but will be set to 0 by PIC for input(as specified in datasheet)
	ADCON1bits.PCFG6 = 1;	//not sure what these next two are, but setting as specified in datasheet
	ADCON1bits.PCFG5 = 1;
	RCSTAbits.SPEN = 1;		//setting serial port enabled
	
	TXSTAbits.SYNC = 0;			//asynchronous mode
//	PIE1.TXIE = 0;

	BAUDCTLbits.BRG16 = 0;	//8 bit transfer
	TXSTAbits.BRGH = 1;		//BRGH high

	TXSTAbits.TXEN = 1;		//enable transmit

  /*
   * Open the USART configured as
   * 8N1, 96000 baud, in polled mode
   */
  OpenUSART (USART_TX_INT_OFF &
             USART_RX_INT_OFF &
             USART_ASYNCH_MODE &
             USART_EIGHT_BIT &
             USART_CONT_RX &
             USART_BRGH_HIGH, 51);   //[8000000/(9600*16)] - 1 = 51

  /* Loop forever */
  while (1)
  {
		//here, we read the USART and store the char in myCache.
		//Once we have read 16 bytes, we have recieved a full RFID tag ID and need to send it out
		//over the transmit.

		c = ReadUSART();
		myCache[counter] = c;
		counter++;

		if(counter >= 15)		    	        //weve read 16 bytes here
		{
			CloseUSART();					    //so we close the USART
	 		 OpenUSART (USART_TX_INT_OFF &	    //and reopen it at 4800 baud
            	 USART_RX_INT_OFF &
            	 USART_ASYNCH_MODE &
            	 USART_EIGHT_BIT &
           	  	 USART_CONT_RX &
            	 USART_BRGH_HIGH, 103);	    	//[8000000/(4800*16)] - 1 = 103
		
			for(j = 0; j<16;j++)                     //in a for loop, we write each char to the output
			{					         //pin of the USART
				WriteUSART(myCache[j]);
			}
			
			counter = 0;		//we set the counter back to 0
			 
			 CloseUSART();					//we then close the USART again
	 		 OpenUSART (USART_TX_INT_OFF &	   //and reopen it back at 9600 baud to
            	 USART_RX_INT_OFF &			         //wait for the next transmission
            	 USART_ASYNCH_MODE &
            	 USART_EIGHT_BIT &
           	  	 USART_CONT_RX &
            	 USART_BRGH_HIGH, 103);		//[8000000/(9600*16)] - 1 = 51
		}
		
  }
}

 

[Pommie]

Shouldn't,

            for(j = 0; j<16;j++) //in a for loop, we write each char to the output
            { //pin of the USART
                WriteUSART(myCache[counter]);
            }

be,

            for(j = 0; j<16;j++) //in a for loop, we write each char to the output
            { //pin of the USART
                WriteUSART(myCache[[COLOR="Red"]j[/COLOR]]);
            }

Mike.

 

[wklose99]

Yea sorry about that this is code I sent my partner last night who tested it(since he has the breadboard setup at his place) and caught that. That has been fixed and it still doesn't work. I am thinking its something to do with my approach and not necessarily a syntax in the coding because I have tried numerous different setups, changing the numbers, delays, etc.

Thank you for your help though!

-WK


note: I edited the original post to fix the error Pommie caught

 

[Pommie]

note: I edited the original post to fix the error Pommie caught

Could you also edit it and put

 before your code and [/co de] after (without the space) so it becomes readable. You will have to recopy the original code so the formating isn't lost.

Mike.

 

[wklose99]

Ahh alright I was wondering if there was someway to clean it up. Thanks much again!

-WK

 

[Pommie]

Why not simplify it,

  while (1)
  {
        //here, we read the USART and store the char in myCache.
        //Once we have read 16 bytes, we have recieved a full RFID tag ID and need to send it out
        //over the transmit.

        OpenUSART (USART_TX_INT_OFF &
                 USART_RX_INT_OFF &
                 USART_ASYNCH_MODE &
                 USART_EIGHT_BIT &
                 USART_CONT_RX &
                 USART_BRGH_HIGH, 51);   //[8000000/(9600*16)] - 1 = 51

        for(j = 0; j<16;j++)                     //in a for loop, we write each char to the output
        {                             //pin of the USART
            myCache[j]=ReadUSART();
        }
        CloseUSART();                        //so we close the USART
        OpenUSART (USART_TX_INT_OFF &        //and reopen it at 4800 baud
            USART_RX_INT_OFF &
            USART_ASYNCH_MODE &
            USART_EIGHT_BIT &
            USART_CONT_RX &
            USART_BRGH_HIGH, 103);            //[8000000/(4800*16)] - 1 = 103        
        for(j = 0; j<16;j++)                     //in a for loop, we write each char to the output
        {                             //pin of the USART
            WriteUSART(myCache[j]);
        }        
        CloseUSART();                        //so we close the USART
    }

See if that works.

Are you sure that the RFID tags are 16 bytes and don't have an additional crlf or something on the end. Do you receive anything on the output?

Mike.

 

[BronzeG3]

Before reading from the UART, you should make sure there is something in the buffer to read.

try

for(counter = 0; counter <= 15;)
{
	if (DataRdyUSART())
	{
		myCache[counter] = ReadUSART();
		counter++;
	}
}

edit: ;'s

 

[wklose99]

Waiting for datareadyUSART() worked. Thanks for all the help!

-WK