Text LCD Enhanced

New features¶

Support for more LCD types
- TextLCD::LCD8x1 8x1 LCD panel
- TextLCD::LCD8x2 8x2 LCD panel
- TextLCD::LCD16x4 16x4 LCD panel
- TextLCD::LCD24x2 24x2 LCD panel
- TextLCD::LCD24x4 24x4 LCD panel (for KS0078 controller)
- TextLCD::LCD40x2 40x2 LCD panel
Support for Cursor and/or Blinking current character
Support for User Defined Characters to display special symbols
Improved methods to get and set the memory address of the current character

Background¶

The LCD driver HD44780 is designed for 2 rows of max 40 chars. Note that it needs some support drivers to control that maximum number of chars.

The address for the first char on the first line is 0x00. The address for the first char on the second line is 0x40. Four line displays are generally created by splitting the two line display and arranging the two parts above eachother. For example 2x40 is split in 2 parts of 2x20 and arranged as 4x20. The adddresses for the 3rd and 4th line just continue where the split was made:

The address for the first char on the first line is 0x00, the last char is 0x13.

The address for the first char on the second line is 0x40, the last char is 0x53.

The address for the first char on the third line is 0x14, the last char is 0x27.

The address for the first char on the fourth line is 0x54, the last char is 0x67.

The original TextLCD lib uses the address(column,row) method to return the memory address. However, the method adds 0x80 to the returned addressvalue to include the 'set display datamemory address' command. This is rather confusing when you try to make sense of the actual address. See discussion here.

The enhanced library provides the getAddress(column,row) method to return the correct address. The original method is still provided for compatibility reasons.

Notes: The HD44780 is pretty flexible and variations of driverhardware and LCD glass layout may result in differences. Some 4 line displays actually use two controllers with separate enable pins. The HD44780 supports left/right shifting of memory locations (address) wrt displayposition. That changes the address of the char that is shown on a displaylocation.

Text LCD Enhanced Library¶

Import library
TextLCD - TextLCD Class Reference

Public Types
enum	LCDType { LCD8x1 , LCD8x2 , LCD16x1 , LCD16x2 , LCD16x2B , LCD16x4 , LCD20x2 , LCD20x4 , LCD24x2 , LCD24x4 , LCD40x2 }
	LCD panel format. More...
enum	LCDCursor { CurOff_BlkOff , CurOn_BlkOff , CurOff_BlkOn , CurOn_BlkOn }
	LCD Cursor control. More...
Public Member Functions
	TextLCD (PinName rs, PinName e, PinName d4, PinName d5, PinName d6, PinName d7, LCDType type=LCD16x2)
	Create a TextLCD interface for using regural mbed pins.
	TextLCD (I2C *i2c, char deviceAddress, LCDType type=LCD16x2)
	Create a TextLCD interface using an I2C PC8574 portexpander.
int	putc (int c)
	Create a TextLCD interface using an SPI 74595 portexpander.
int	printf (const char *format,...)
	Write a formated string to the LCD.
void	locate (int column, int row)
	Locate to a screen column and row.
int	getAddress (int column, int row)
	Return the memoryaddress of screen column and row location.
void	setAddress (int column, int row)
	Set the memoryaddress of screen column and row location.
void	cls ()
	Clear the screen and locate to 0,0.
int	rows ()
	Return the number of rows.
int	columns ()
	Return the number of columns.
void	setCursor ( LCDCursor show)
	Set the Cursormode.
void	setUDC (unsigned char c, char *udc_data)
	Set User Defined Characters.
Protected Types
enum	_LCDBus { _PinBus , _I2CBus , _SPIBus }
	LCD Bus control. More...
Protected Member Functions
void	_init ()
	Init the LCD controller 4-bit mode, number of lines, no cursor etc Clear display.

Example Code¶

// Hello World! for the TextLCD

#include "mbed.h"
#include "TextLCD.h"

// Host PC Communication channels
Serial pc(USBTX, USBRX); // tx, rx

//TextLCD lcd(p15, p16, p17, p18, p19, p20, TextLCD::LCD16x4); // rs, e, d4-d7 ok
//TextLCD lcd(p15, p16, p17, p18, p19, p20, TextLCD::LCD20x2); // rs, e, d4-d7 ok
TextLCD lcd(p15, p16, p17, p18, p19, p20, TextLCD::LCD20x4); // rs, e, d4-d7 ok
//TextLCD lcd(p15, p16, p17, p18, p19, p20, TextLCD::LCD24x2); // rs, e, d4-d7 ok
//TextLCD lcd(p15, p16, p17, p18, p19, p20, TextLCD::LCD40x2); // rs, e, d4-d7 ok

int main() {
    pc.printf("LCD Test. Columns=%d, Rows=%d\n\r", lcd.columns(), lcd.rows());
    
    for (int row=0; row<lcd.rows(); row++) {
      int col=0;
      
      pc.printf("MemAddr(Col=%d, Row=%d)=0x%02X\n\r", col, row, lcd.getAddress(col, row));      
//      lcd.putc('-');
      lcd.putc('0' + row);      
      
      for (col=1; col<lcd.columns()-1; col++) {    
        lcd.putc('*');
      }

      pc.printf("MemAddr(Col=%d, Row=%d)=0x%02X\n\r", col, row, lcd.getAddress(col, row));      
      lcd.putc('+');
        
    }    
    
// Show cursor as blinking character
    lcd.setCursor(TextLCD::CurOff_BlkOn);

// Set and show user defined characters. A maximum of 8 UDCs are supported by the HD44780.
// They are defined by a 5x7 bitpattern. 
    lcd.setUDC(0, (char *) udc_0);  // Show |>
    lcd.putc(0);    
    lcd.setUDC(1, (char *) udc_1);  // Show <|
    lcd.putc(1);    
    lcd.setUDC(2, (char *) udc_2);
    lcd.putc(2);    
    lcd.setUDC(3, (char *) udc_3);
    lcd.putc(3);    
    lcd.setUDC(4, (char *) udc_4);
    lcd.putc(4);    
    lcd.setUDC(5, (char *) udc_5);
    lcd.putc(5);    
    lcd.setUDC(6, (char *) udc_6);
    lcd.putc(6);    
    lcd.setUDC(7, (char *) udc_7);
    lcd.putc(7);  
 
}

The terminal will print the actual memory addresses like this:

LCD Test. Columns=20, Rows=4

MemAddr(Col=0, Row=0)=0x00

MemAddr(Col=19, Row=0)=0x13

MemAddr(Col=0, Row=1)=0x40

MemAddr(Col=19, Row=1)=0x53

MemAddr(Col=0, Row=2)=0x14

MemAddr(Col=19, Row=2)=0x27

MemAddr(Col=0, Row=3)=0x54

MemAddr(Col=19, Row=3)=0x67