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EUSART Serial Communication help

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gwntd

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Hi, I'm new to programming with the pic, so I've been having some trouble setting up a serial communication, EUSART1, from my pic to my computer. I am using the pic18f27j13 with a max232 to try and send signals at a baudrate of 115200 to the computer. I'm using realterm to read the signals. But, non-correct Hex values are being read. My attempt is to set the Fosc to be 48Mhz from the internal clock and a baudrate of 115200. Can anyone kindly help me by looking at my code and pointing out any mistakes that I may have made. Thank you.

Some funky things that I have noticed with realterm. Is that if I send 0x88 it comes out as 0xFA // 1000 1000 -> and get 1111 1010.
0x00 -> gets 0xF0
0xFF -> gets 0xFF
0x1F -> gets 0xF3

I really don't see any pattern.
Code: 
#include <p18f27j13.h>
#include <stdio.h>

#pragma config WDTEN = OFF   // Sets watchdog OFF
#pragma config PLLDIV = 2 	 // Sets divider to 2. Provides output 4Mhz for 96Mhz PLL
#pragma config OSC = INTOSCPLL // Sets OSC as INTOSC(8Mhz) Postscalled with a PLL
#pragma config CFGPLLEN = ON //enables PLL on startup
#pragma config PLLSEL = PLL96 // selects 96Mhz
#pragma config XINST = OFF
 

// setup functions
void delay();
void Wait_Buffer1();
void setupUSART();

//

void delay ()
{
	unsigned long int count = 0;
	for (count = 0; count < 0x0003FFFF; count ++)
	{
	}
}

void Wait_Buffer1(void) 
{
	while (!TXSTA1bits.TRMT) 
	{}
}	
void setupUSART()
{

	OSCCONbits.SCS = 0x00; // Selects Primary clock(FOSC) as the clock source


	stdout = _H_USART;

    TXSTA =   0b00100000; //Enable transmit and low baud rate
    RCSTA =   0b10010000; //Enable serial port
    BAUDCON = 0b00001000; //Enable 16 bit baud generator
    
    SPBRGH = 0;
    SPBRG = 25;

	//target baudrate 115200, 

}


void main ()
{
	unsigned int loop_count = 0;
	TRISCbits.TRISC7 = 1;
	TRISCbits.TRISC6 = 0;
	setupUSART();

	while (1)
	{
	delay();
	TXREG1 = 0x1F;
	delay();

	
		
	}
}
 

you are calculating bit rate based on 48Mhz, but setting the PLL to 96MHz
#pragma config PLLSEL = PLL96 // selects 96Mhz
 

I wasn't sure because based on the data sheet from the diagram. On page 36, I was thinking selecting 96Mhz will automatically mean that it will get divided by 2. Is it true that this is not the case? So I should set #pragma config PLLSEL = PLL96 --> #pragma config PLLSEL = PLL48

--Edit- I've rechecked the data sheet. There are only two selections for the PLLSEL, which is PLL96 and 4xPLL. The latter which does not serve my intended purpose of 48Mhz Fosc. So I believe setting PLLSEL = PLL96 should be correct.
 
Last edited:

Gwntd, your oscillator settings and baud rate look correct to me. 8MHz internal clock, fed through the PLL Prescaler at /2 and the finally-resulting 48MHz selected as system clock (with OSCCON at default value 00)

(I use CCS myself though, so I'm not used to setting the configuration directly. I've done a quick review of the datasheet regarding all the oscillator configuration registers but I might have missed something. Just covering my back, lol.)

So, provided the internal oscillator is accurate enough, and the datasheet says it is typically 0.15%, then I don't see what is wrong.

Have you tried using a much lower baud rate to test? That's what I do in serial problems - try 9600 baud and see if that works reliably.

Do you have an oscilloscope that you could check the serial timing with?
 
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    gwntd

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FoxyRick said:
Gwntd, your oscillator settings and baud rate look correct to me. 8MHz internal clock, fed through the PLL Prescaler at /2 and the finally-resulting 48MHz selected as system clock (with OSCCON at default value 00)

(I use CCS myself though, so I'm not used to setting the configuration directly. I've done a quick review of the datasheet regarding all the oscillator configuration registers but I might have missed something. Just covering my back, lol.)

So, provided the internal oscillator is accurate enough, and the datasheet says it is typically 0.15%, then I don't see what is wrong.

Have you tried using a much lower baud rate to test? That's what I do in serial problems - try 9600 baud and see if that works reliably.

Do you have an oscilloscope that you could check the serial timing with?
Click to expand...

Thank you so much, setting the baud rate to 9600 did work for characters F0 - FE. And I am reading the correct values. However this is only at a baudrate of 57600 read from realterm. and any other charcters F0 and down, will usually generate a framing error. So I am assuming that my Fosc is generated as correctly as as i assumed. I'm attempting to see how off I am with a oscilloscope, but I don't have too much experience with it.
When operating at 9600 for realterm, i end up getting no signals at all.

I've made some progress. By setting the baudrate to 57600 on the pic, I can transmit and receive all signals correctly. :shock:

But when setting 9600 baudrate on the pic, I can only transmit and recieve signals 0xF0-FF.
 
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