USART on PIC16F628A

[hazzer123]

Hi

I am trying to write some code, in assembly, to communcate serially between a PIC17F628a and HyperTerminal.

The PIC has an inbuilt USART, but i was just wondering, will i have to use something like a MAX232 to lower the voltages coming from my computer, + and - 12V, in order for the PIC to be safe.

Another thing - the signals coming out of the PC are reversed, a high signal is -12V and vice versa. Will this need to be inverted for the USART  in the PIC to receive it or do USARTs automatically do this?

Thankyou

[JonHylands]

The MAX232 will automatically handle inverting the data, and translating the voltages appropriately...

- Jon

[Hal9000]

Code: [Select]

#include <pic.h>
#include <stdio.h>
#include "usart.h"

/********************************************************************************************************************************
 * Author: Ian Robinson *
 * Date Created: December 2006 *
 * Project: EG3001 Project1 : Ultrasonic 3D position location *
 * Project Synopsis: A project to show ultrasonic 3D position location over an RS-232 link using the principle of trilateration *
 ********************************************************************************************************************************/

__CONFIG(BORDIS & UNPROTECT & MCLRDIS & PWRTEN & WDTDIS & INTIO);

#define PORTBIT(adr, bit) ((unsigned)(&adr)*8+(bit))

static bit LED0 @ PORTBIT(PORTB, 0);
// B1 used for RX
// B2 used for TX
static bit LED3 @ PORTBIT(PORTB, 3);
static bit RX1 @ PORTBIT(PORTB, 4); // RX1 (RB4) TOP RIGHT
static bit RX2 @ PORTBIT(PORTB, 5); // RX2 (RB5) BOTTOM RIGHT
static bit RX3 @ PORTBIT(PORTB, 6); // RX3 (RB6) TOP LEFT  (SET AS INPUTS WHEN TIMER 1 FUNCTIONS)
static bit RX4 @ PORTBIT(PORTB, 7); // RX4 (RB7) BOTTOM LEFT (SET AS INPUTS WHEN TIMER 1 FUNCTIONS)

//TRISB4 =1; //Put RB4 into input mode
//TRISB5 =1; //Put RB5 into input mode
//TRISB6 =1; //Put RB6 into input mode
//TRISB7 =1; //Put RB7 into input mode

/***********************************************Variable Declaration************************************************************/

unsigned int i,j; //for loop pause
unsigned int timerReading;
unsigned int timerReadingRX1;
unsigned int timerReadingRX2;
unsigned int compare;

/***********************************************Function Declaration************************************************************/
void initialRecieve(void);
void check1(void);
void check2(void);
/***********************************************Main Function*******************************************************************/

void main(void){

unsigned char input;

INTCON=0; // purpose of disabling the interrupts.

init_comms(); // set up the USART - settings defined in usart.h

TRISB7 = 0;

T1CON = 0b00001100; // Timer 1 control register set-up
TMR1H = 0; // Clear high bit
TMR1L = 0; // Clear low bit
T1OSCEN = 0; // Disable Built-in oscillator between RB6 and RB7
GIE = 1; // enable global interrupts
PEIE = 1; // enable peripheral interrupts

TMR1IF = 0; // clear Timer 1 interrupt flag
TMR1ON = 1; // start Timer 1
TMR1IE = 1; // enable Timer 1 interrupt

timerReading = 0;
compare = 0;

/***********************************************While Loop*********************************************************************/

while(1){

// initialRecieve();

// TMR1ON = 0;
// timerReading = (TMR1H << 8) + TMR1L;
// TMR1ON = 1;
// printf("%10u\t",timerReading);


if(RB7 == 0)
{
//printf("%10u\t",timerReading);
printf("RB7");
}

}
}

/***********************************************End of Main and While Loop**************************************************************/

/***********************************************Initial Recieve Function****************************************************************/

void initialRecieve(void){

while(1)
{
if(RX1 == 0)
{
timerReadingRX1 = 0;
TMR1ON = 1;
check2();
}
else if(RX2 == 0)
{
timerReadingRX2 = 0;
TMR1ON = 1;
check1();
}
}
}

/***********************************************Check for 1 Function****************************************************************/

void check1(void){

while(RX1 != 0)
{
if(RX1 == 0)
{
TMR1ON = 0;
timerReadingRX1 = (TMR1H << 8) + TMR1L;
printf("%10u\nTX1 is",timerReading, "TX2 is 0");
timerReading = 0;
}
}
}

/***********************************************Check for 2 Function****************************************************************/

void check2(void){

while(RX2 != 0)
{
if(RX2 == 0)
{
TMR1ON = 0;
timerReadingRX2 = (TMR1H << 8) + TMR1L;
printf("%10u\nTX2",timerReading, "TX1 is 0");
timerReading = 0;

}
}
}

/***********************************************Calculate Distances****************************************************************/

void calculate(void){


}




/***********************************************Delay Function****************************************************************/

void delay()
{

for(i=0; i<4000; i++)
{
for(j=0; j<30; j++)
{
}
}

}

/***********************************************Interrupt (ISR) Routine*********************************************************/

void interrupt tmr1int(void)
{
if(TMR1IF)
{
TMR1IF=0;
timerReading = 0;
}
}

/**************************************************END OF CODE****************************************************************/


The printf statement sends stuff to hyperterminal.

Take what you like from the code. I was using the same PIC.

Good luck