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Serial LCD Library

LCD display 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.

The following files are referenced below, but for simplicity I've listed them here for download: The following routines are defined:

  • void lcd_putc(char c) send the byte c to the LCD
  • void lcd_clear(void) clears the LCD screen
  • void lcd_home(void) homes the LCD cursor
  • void lcd_puts() print a string **UNIMPLEMENTED**
  • void lcd_printhex(char c) prints byte c as a 2 digit hex character
  • void lcd_printdec(char c) prints byte c as a decimal digit string
  • void lcd_printbin(char c) prints byte c as a binary string
  • void lcd_scroll_left(char n) scrolls LCD screen left n positions
  • void lcd_scroll_right(char n) scrolls LCD screen right n positions
  • void lcd_goto(char row, char col) goto a location
The LCDPORT and LCDPIN constants define which port and logical pin the serial LCD is connected to. By default they are set to PORTA and pin 1 which is the RA1 output on phsyical pin 17 of a PICC84.

If you connect the serial LCD to a different port and pin then you must change the definitions in the lcd.c file.
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_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.

Using the library

The Makefile for this library is as follows:
# Makefile for LCD test code
# Mark Crosbie 9/15/98
# mark@mastincrosbie.com

ASMINCS= p16c84.inc 

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  -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  -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  -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  -olcdtest4.asm lcd.lib delays.lib lcdtest4.c

lcd.lib: lcd.c
	c2c  -lib -olcd.lib lcd.c

delays.lib: delays.c
	c2c  -lib -odelays.lib delays.c

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

Example 1 - Printing numbers

The lcdtest1.c 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.

Example 2 - Printing at a location

lcdtest2.c shows how to position the cursor at a specific location and print information. 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.

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.

PIC Microcontroller Project Book
Lot's of great PIC project ideas!

Programming and Customizing the Pic Microcontroller

If you are learning to program microcontrollers then Myke's book is good start.
The Art of Electronics
A classic in the field. Teaches you the art and science of linear and digital electronic design. If you want to learn why your circuit is not working, read this book and you'll know why.
Mobile Robots: Inspiration to Implementation
A very readable introduction to the art of robotic design and implementation from the best practioners in the field: the MIT Artificial Intelligence Lab!
Microcontroller Cookbook
A set of cookbook style designs for the 8051 and PIC microcontrollers. A handy reference to have if you need a quick solution to a problem.

© 2002-2004 Mark Crosbie   shareright © 2002 Phlash