Interface to a Serial LCD

Here is a library to interface your PIC code to an LCD that is controlled via a serial line. One such LCD is available from Scott Edwards Electronics. There are many others, and the code shown here can easily be adpated to other LCD displays by changing some defines.

LCD Library Source Code

Here is my library source code.

Or you can download all the files referenced on this page (a gzip'd tar file). For DOS/Windows users, you can download LCDlib.zip in ZIP format.

The following routines are defined:

I'll describe each routines briefly, but they are very simple to understand.

void lcd_putc(char c) - send a byte to the LCD

This routine is the heart of the LCD library: it will send a byte specified in the argument c to the LCD connected to the port defined by LCDPORT and pin LCDPIN. All the other routines use this code.

lcd_putc() assumes that the LCD is running at 9600 baud, 8-N-1 serial settings. If your LCD is running at a different baud rate, or you have a faster PIC, you will have to adjust the timing loop starting at lcdtxloop.

The lcd_putc() routine places a 10ms pacing delay between each character.

void lcd_clear(void) - clear the LCD screen

Building upon the lcd_putc() routine is easy, as this routine shows. We simply send the byte sequence that clears the display.

void lcd_home(void) - home the LCD cursor

Sends the byte sequence that homes the LCD cursor to the top left hand corner.

void lcd_puts() - print a string **UNIMPLEMENTED**

This function will print a string on the display. Unfortunately, the C2C compiler currently does not support pointers, so there is no easy way to write this code. I'm working on this...

void lcd_printhex(char c) - print byte as hex

Print a byte value on the display as 2 hex characters. For example, the value 255 would be printed as FF. The code prints the hi nibble first (the upper 4 bits of the byte), followed by the lower nibble.

void lcd_printdec(char c) - print byte as decimal

Print a byte value as a decimal string. For example, the value 123 is printed as the characters "123". This function performs repeated subtractions: starting at 100, we subtract until the value left is less than 100. We then repeat the loop for 10's. Whatever is left is the units value. Effectively, this routine performs division by repeated subtraction.

The output of lcd_printdec() is always 3 digits long: 001 as against just 1.

void lcd_printbin(char c) - print byte as binary

This routine prints a binary representation of a byte. For example, 129 would be printed as 10000001. 8 bits are always printed, which means that the value may have leading zeros: 5 would be printed as 00000101.

void lcd_scroll_left(char n) - scroll screen left

Scroll the LCD display left n positions. The effect of this command depends a lot on the type of LCD display you have.

void lcd_scroll_right(char n) - scroll screen right

Scroll the LCD display right n positions. The effect of this command depends a lot on the type of LCD display you have.

void lcd_goto(char row, char col) - goto a position

Positions the cursor at the specified row and column. The row argument starts at 0. So the first line on a two line LCD is row 0, and the second line is row 1. Similarly, the col argument starts at 0.

If you print off the screen, it is not displayed, but is stored in the LCD's RAM. Use the lcd_scroll_left and lcd_scroll_right commands to access the data.

Examples of how to use the library

Here is some sample code using the LCD library. A schematic for wiring this up looks as follows:

lcd test schematic

The Makefile for this library is as follows: 

#
# Makefile for LCD test code
#
# Mark Crosbie 9/15/98
#

LIBS=lcd.lib
ASMINCS= p16c84.inc 
C2CINCS= 


all: lcdtest1.hex lcdtest2.hex lcdtest3.hex

lcdtest1.hex: lcdtest1.asm
	gpasm -r dec -p 16c84 -t lcdtest1.asm
lcdtest1.asm: lcdtest1.c lcd.lib delays.lib
	c2c ${C2CINCS} -olcdtest1.asm lcd.lib delays.lib lcdtest1.c

lcdtest2.hex: lcdtest2.asm
	gpasm -r dec -p 16c84 -t lcdtest2.asm
lcdtest2.asm: lcdtest2.c lcd.lib delays.lib
	c2c ${C2CINCS} -olcdtest2.asm lcd.lib delays.lib lcdtest2.c

lcdtest3.hex: lcdtest3.asm
	gpasm -r dec -p 16c84 -t lcdtest3.asm
lcdtest3.asm: lcdtest3.c lcd.lib delays.lib
	c2c ${C2CINCS} -olcdtest3.asm lcd.lib delays.lib lcdtest3.c

lcdtest4.hex: lcdtest4.asm
	gpasm -r dec -p 16c84 -t lcdtest4.asm
lcdtest4.asm: lcdtest4.c lcd.lib delays.lib
	c2c ${C2CINCS} -olcdtest4.asm lcd.lib delays.lib lcdtest4.c


lcd.lib: lcd.c
	c2c ${C2CINCS} -lib -olcd.lib lcd.c

delays.lib: delays.c
	c2c ${C2CINCS} -lib -odelays.lib delays.c

clean:
	rm *.hex *.lib core *.asm *.lst

Example 1 - Printing numbers

The source code for this test case is available. This test prints the numbers between 32 and 128 as an ASCII character, a decimal number and a hex number. There is a 1 second delay each time through the loop so you can see the output. The code is quite simple: first the PORTA pin to which the LCD is connected is set to be an output. The code then delays for a second to give the LCD a chance to initialize (it really only needs a few 100 milliseconds). Then the LCD is cleared using lcd_clear().

The loop iterates through the ASCII characters between 32 and 128 and prints each one as a character, a decimal value and a hex value.

The hex output file is available for a PIC 16C84. 

/*
 * lcdtest1.c
 *
 * Test lcd.lib and delays.lib
 *
 * Shows the operation of lcd_putc, lcd_printdec and lcd_printhex
 *
 * Connect the LCD to port A pin 1 (i.e. physical pin 18 on a 16C84)
 *
 * Mark Crosbie 9/15/98
 */

#define LCDPIN 1

void main(void) {

  char i;

  set_bit(STATUS, RP0);    /* select the register bank 1 */
  clear_bit(TRISA, LCDPIN);  /* Port A is output */
  clear_bit(STATUS, RP0);

  delay_s(1);

  lcd_clear();
  delay_s(1);

  while(1) {
    for(i=32; i < 128; i++) {
            lcd_putc(i);
	    lcd_putc(' ');
	    lcd_printdec(i);
	    lcd_putc(' ');
            lcd_printhex(i);
      delay_s(1);
      lcd_clear();
    }
  }
}

Example 2 - Printing at a location

This example shows how to position the cursor at a specific location and print information. The source code is available. It uses the previous example's loop and adds lcd_goto() calls between each print.

The assembly output is available, as is the hex output file for a PIC 16C84. 

/*
 * lcdtest2.c
 *
 * Test lcd.lib and delays.lib
 * 
 * Shows the operation of lcd_goto to position cursor
 *
 * Connect the LCD to port A pin 1 (i.e. physical pin 18 on a 16C84)
 *
 * Mark Crosbie 9/20/98
 */

#define LCDPIN 1

void main(void) {

  char i;

  set_bit(STATUS, RP0);    // select the register bank 1
  clear_bit(TRISA, LCDPIN);           // Port A is output
  clear_bit(STATUS, RP0);

  delay_s(1);

  lcd_clear();
  delay_s(1);
  while(1) {
    for(i=32; i < 128; i++) {
            lcd_putc(i);
	    lcd_goto(0,5);
	    lcd_printdec(i);
	    lcd_goto(0,10);
            lcd_printhex(i);
            lcd_goto(1,2);  /* goto row 1 col 5 */
	    lcd_printbin(i);
      delay_s(1);
      lcd_clear();
    }
  }
}

Example 3 - Scrolling the LCD

We now test the scrolling commands to scroll the LCD left and right. My LCD can only display 16 columns of text, but if you continue to print, the extra characters are still stored in the LCD's RAM, but are not displayed. However, if you scroll the LCD left you can display the characters off the screen.

This simple example prints 32 characters to the first row on the LCD. It then scrolls the LCD left a character at a time, and then right a character at a time.

The source code is available, as is the generated assembly output and the hex output file. 

/*
 * lcdtest3.c
 *
 * Test lcd.lib and delays.lib
 * 
 * Shows the operation of lcd_scroll_left and lcd_scroll_right
 * commands
 *
 * Prints out the first 32 characters of the ASCII character set. Only 
 * the first 16 show on my LCD, so I scroll left by 16
 * characters. Then I scroll back right by 16 characters.
 *
 * Connect the LCD to port A pin 1 (i.e. physical pin 18 on a 16C84)
 *
 * Mark Crosbie 9/20/98
 */

#define LCDPIN 1

void main(void) {

  char i;

  set_bit(STATUS, RP0);    // select the register bank 1
  clear_bit(TRISA, LCDPIN);           // Port A is output
  clear_bit(STATUS, RP0);

  delay_s(1);

  lcd_clear();
  delay_s(1);
  while(1) {
    for(i=32; i < 64; i++) {
            lcd_putc(i);
    }
    delay_s(1);
    for(i=0; i < 16; i++) {
      lcd_scroll_left(1);
      delay_ms(200);
    }
    delay_s(2);
    for(i=0; i < 16; i++) {
      lcd_scroll_right(1);
      delay_ms(200);
    }
    delay_s(2);
    lcd_clear();
    
  }
}


    

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Last modified on Dec 1, 1998 by 
Mark Crosbie (mcrosbie@best.com)