Hi All,

I'm trying to get serial communications between two PICs to work.  Below is
the code I have come up with to get the job done.  The way I have the
circuit set up is as follows:

Both PIC 16F627's are wired identically with the exception of RB0.  PIC1's
RB0 pin is pulled high, telling it to transmit serial data.  PIC2's RB0 pin
is pulled low to tell it not to send data.  MCLR is pulled high with a 10K
resistor.  RA0-RA4 are output pins which are connected to the cathode
(negative) side of five LEDs.  The LEDs each have a 330 Ohm resistor
connected to VCC (+5v) on the Anode side.  PIC1's TX pin (RB2) is connected
to PIC2's RX pin (RB1).  PIC1's RX pin (RB1) is connected to PIC2's TX pin
(RB2).

I am using PICC Lite to program the PICs.  I am also using interrupt
routines to determine when data needs to be transmitted or received.  I
delay for a while in between each byte sent so I can see what is being sent
and what is being received.  I have configured the PICs to use the internal
4Mhz clock, disabled the watch dog timer, enabled the power up timer,
enabled the memory clear bit, enabled the brown out detection, and
unprotected the code and memory.  The code is a modified version of one of
Myke Predko's sample routines.  As of right now, when I give power to the
circuit, all five LEDs connected to PORTA are lit up and stay that way
forever.  Any help you could give me is greatly appreciated.

Scott Pierce


#include <pic.h>
unsigned char Data = 0;

//=============================================================================

__CONFIG (INTIO & WDTDIS & PWRTEN & MCLREN & BOREN & DATUNPROT & UNPROTECT);

//=============================================================================

void interrupt InterrupRoutine (void)
{
        if (TXIF)        //if Transmit interrupt flag is set
        {
                TXIF  = 0;               //Reset Interrupt
                TXREG = Data;  //Send Data

   }//if

   if (RCIF)         //if Receive interrupt flag is set
   {
     RCIF  = 0;     //Reset Interrupt Request
     PORTA = ~RCREG; //Set PORTA equal to serial receive buffer

   }//if

}//InterruptRoutine

//=============================================================================

void Delay(void)
{
        unsigned char i = 0;

   for (i = 0; i < 250; i++)
   {} //do nothing

}//Delay

//=============================================================================

void main(void)
{
   //unsigned char temp;
   unsigned char i = 0;

   TRISA = 0b00000000; //set PORTA to all outputs
   TRISB = 0b00000011; //set pins 0 & 1 on PORTB to inputs, rest outputs

   OPTION = 0x0D1; //Assign Prescaler to TMR0
                   //Prescaler is /4
   TMR0 = 0;       //Reset the Timer for Start
   T0IE = 1;       //Enable Timer Interrupts
   GIE  = 1;       //Enable Interrupts

   SPBRG = 51;     //1200 bps @ 4 MHz
   TXEN = 1;       //Enable the USART
   CREN = 1;
   SPEN = 1;

   PEIE = 1;       //Enable PIE Interrupt Sources

   //temp = RCREG;
   RCIF = 0;       //Clear Receive Interrupt Flag
   RCIE = 1;       //Enable Receive Interrupt

   TXIF = 0;       //Clear Transmit Interrupt Flag
   TXIE = 1;       //Enable Transmit Interrupt

   PORTA = ~0;     //Clear PORTA (LEDs cathode pins are connected to PORTA)
                   //LED Anode pins are connected to VCC thru 330 Ohm Resistors

   Data = 0;

   while (1 == 1)
        {
     if (RB0 == 1)
     {
       for (i = 0; i < 250; i++) //delay before sending the next byte so we can
         Delay();                // see each byte being sent

       Data++;

       if (Data > 31)   //since we're only displaying 5 bits, we'll only send
         Data = 0;      //  values 0 thru 31

       PORTA = ~Data; //display what we're sending on PORTA
       TXIF = 1;      //set Transmit interrupt flag

       for (i = 0; i < 250; i++) //delay after sending byte so we can see each
         Delay();                // byte being sent

     }//if

        }//while

}//main

//=============================================================================

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