Data problem on PIC16F616 (To LCD)

[Madsaaby]

Hey Folks

I have a problem with the PIC16F616. I'm trying to drive a LDC Display (HD44780) in 4 Bit mode (To display temps, but nothing else than the display is connected yet.).

I noticed that the data on two of the lines were bad.. The high bits were only 400 us long, while they were 2 ms on the other two..

So, I tried changing different things, making sure ADC, timers, comparators were off etc. Nothing solved the problem, until I selected a different output pin on the MCU, then the data became fine..

I'm getting the same problem on the following pins: RA1,RA2, RC1-RC4.

It's the first time I use the 16F616, so I might have missed something.. I did try the same lcd driver on the PIC16F628a where it worked fine..

I guess its not the driver thats bad when it helps to select a different pin ?

Any ideas why this happens, only on some pins  ?
Ask if you need more info, I know I didn't tell much, but don't really know where the problem comes from.. :/


I use the HI-Tech C compiler, and the following LCD Driver and C code..
(I've put in some delays to separate things a little)

C Code:

#include <htc.h>
#include "lcd.h"
#include <stdio.h>
#include <stdlib.h>

#ifndef _XTAL_FREQ

  #define _XTAL_FREQ 4000000

#endif




void
main()
{

   
   // CMCON = 0xff;
   T1CON =0;
   C1ON =0;
   C2ON =0;
   ADON =0;
   TRISA= 0x00;
   TRISC= 0x00;
   

        __delay_us(100);
   lcd_init();
   __delay_us(100);
//      lcd_goto(0);                     
//   lcd_puts("Random Shit");
//   lcd_goto(0x40);                        
//   lcd_puts("0101010");
   

}



Driver:



/*
 *   LCD interface example
 *   Uses routines from delay.c
 *   This code will interface to a standard LCD controller
 *   like the Hitachi HD44780. It uses it in 4 bit mode, with
 *   the hardware connected as follows (the standard 14 pin
 *   LCD connector is used):
 *   
 *   PORTB bits 0-3 are connected to the LCD data bits 4-7 (high nibble)
 *   PORTA bit 2 is connected to the LCD RS input (register select)
 *   PORTA bit 3 is connected to the LCD EN bit (enable)
 *   
 *   To use these routines, set up the port I/O (TRISA, TRISB) then
 *   call lcd_init(), then other routines as required.
 *
 * Copywrite Craig Lee 1998
 *   
 */

#define _XTAL_FREQ 4000000

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

#define LCD_RS RC4   // Register select
#define LCD_EN RA4   // Enable
#define LCD_D4 RC1   // Data bits
#define LCD_D5 RA0   // Data bits
#define LCD_D6 RC5   // Data bits
#define LCD_D7 RA5   // Data bits

#define   LCD_STROBE   ((LCD_EN = 1),(__delay_us(200)),(LCD_EN=0))



/* write a byte to the LCD in 4 bit mode */

void
lcd_write(unsigned char c)
{
__delay_us(100);
   if(c & 0x80) LCD_D7=1; else LCD_D7=0;
   if(c & 0x40) LCD_D6=1; else LCD_D6=0;
   if(c & 0x20) LCD_D5=1; else LCD_D5=0;
   if(c & 0x10) LCD_D4=1; else LCD_D4=0;
   __delay_us(100);
   LCD_STROBE;
   if(c & 0x08) LCD_D7=1; else LCD_D7=0;
   if(c & 0x04) LCD_D6=1; else LCD_D6=0;
   if(c & 0x02) LCD_D5=1; else LCD_D5=0;
   if(c & 0x01) LCD_D4=1; else LCD_D4=0;
   __delay_us(100);
   LCD_STROBE;   
   __delay_us(40);
}

/*
 *    Clear and home the LCD
 */

void
lcd_clear(void)
{
   LCD_RS = 0;

   lcd_write(0x1);
   __delay_ms(2);
}

/* write a string of chars to the LCD */

void
lcd_puts(const char * s)
{
   LCD_RS = 1;   // write characters
   __delay_us(100);
   while(*s) lcd_write(*s++);
}

/* write one character to the LCD */

void
lcd_putch(unsigned char c)
{
   LCD_RS = 1;   // write characters

   lcd_write(c);
}


/*
 * Go to the specified position
 */

void
lcd_goto(unsigned char pos)
{
__delay_us(100);
   LCD_RS = 0;
__delay_us(100);
   lcd_write(0x80 + pos);
__delay_us(100);
}
   
/* initialise the LCD - put into 4 bit mode */

void
lcd_init(void)
{
   LCD_RS = 0;   // write control bytes

   __delay_ms(15);// power on delay

   LCD_D4 = 1;   // init!   
   LCD_D5 = 1; //
__delay_us(100);
   LCD_STROBE;   
   __delay_ms(5);

   LCD_STROBE;   // init!   
   __delay_us(100);

   LCD_STROBE;   // init!   
   __delay_ms(5);

   LCD_D4 = 0;   // set 4 bit mode
__delay_us(100);
   LCD_STROBE;   
   __delay_us(40);
   
   lcd_write(0x28);// 4 bit mode, 1/16 duty, 5x8 font, 2lines
   lcd_write(0x0C);// display on
   lcd_write(0x06);// entry mode advance cursor
   lcd_write(0x01);// clear display and reset cursor
}

Best regards
Mads

[baljemmett]

So, I tried changing different things, making sure ADC, timers, comparators were off etc. Nothing solved the problem, until I selected a different output pin on the MCU, then the data became fine..

I see your code turns the ADC and comparators off, but you don't clear the ANSEL register -- it defaults to all-ones at power up (so all analogue-capable pins are set as analogue inputs).  Not sure whether that will interfere with digital output at all, but it might be worth chucking an ANSEL = 0; in there to see if it makes any difference?

Ah - I see you're doing bit operations on the output pins - on the PIC that's a read-modify-write operation, i.e. rather than just setting the relevant bit in the output latch it reads the digital state of the port as a whole, changes the specified bit, and then writes the result to the output latch.  A pin configured as an analogue input will always read 0 on the digital side, so I suspect as soon as you try to set a bit on a given port any other analogue pins on that port will go to 0 at the same time.

[Madsaaby]

I see your code turns the ADC and comparators off, but you don't clear the ANSEL register -- it defaults to all-ones at power up (so all analogue-capable pins are set as analogue inputs).  Not sure whether that will interfere with digital output at all, but it might be worth chucking an ANSEL = 0; in there to see if it makes any difference?

Ah - I see you're doing bit operations on the output pins - on the PIC that's a read-modify-write operation, i.e. rather than just setting the relevant bit in the output latch it reads the digital state of the port as a whole, changes the specified bit, and then writes the result to the output latch.  A pin configured as an analogue input will always read 0 on the digital side, so I suspect as soon as you try to set a bit on a given port any other analogue pins on that port will go to 0 at the same time.

Hi baljemmett

Thank you very much, I must have missed the ANSEL register while skimming through the datasheet (And didn't know of its existence )..
It's working just fine after clearing those bits
I have a lot yet to learn, I see. Didn't know about the "whole port" read, modify, write either..
Thanks again for the help, and for the well explained answer

Best regards
Mads

[dcel]

How is the Battle going? Anything useful and/or functional? I have a tube full of pic16f616 that I intend to drive the box full of 8x2 lcds that I got at the swapmeet. I figure that it would be a cool starter project to get an adc set up to measure voltage and display that on the 8x2 lcd. Problem is I just havent the time to get into the lab lately.

Chris 

[Madsaaby]

How is the Battle going? Anything useful and/or functional? I have a tube full of pic16f616 that I intend to drive the box full of 8x2 lcds that I got at the swapmeet. I figure that it would be a cool starter project to get an adc set up to measure voltage and display that on the 8x2 lcd. Problem is I just havent the time to get into the lab lately.

Chris

Hi Chris

The PIC16f616's are running sweet, after I set the ANSEL register correctly . I also got a whole tube of them, and find them quite nice for small projects. The only disadvantage I found is that it's missing eeprom. I did finish my temp display, and also made a small analog PSU with digital voltage and amp reading.. I am currently working on a small but very loud alarm clock, all of them including the 16F616.. I'm sure you will find good use for the mcu's, sounds like a nice project..

-Mads