Silicon Labs / MemoryLCD

Display driver for Sharp's range of SPI-driven memory LCD's, leveraging the power of asynchronous transfers. Currently supports LS013B7DH03, but easily extendable to other models as well.

Dependents:   memLCD-Demo memLCD-Demo memLCD-Demo MemLCD-Temperature-Humidity-Demo ... more

Caution

This library builds upon the asynchronous SPI interface provided by mbed, but not all platforms currently support this. So, make sure your platform is capable of asynchronous SPI (all Silicon Labs platforms are), otherwise you will get compiler errors!

Usage

The library is purposefully quite simple to use. To set it up, you initialize an SPI object and the required I/O pins, and call the library constructor with those. Make sure the display is powered on, enabled, and the inversion mode is set to external (EXTMODE is high).

#define SCK     PD2
#define MOSI 	PD0

DigitalOut CS(PD3);
DigitalOut EXTCOM(PC4);

SPI displaySPI(MOSI, NC, SCK);
silabs::LS013B7DH03 display(&displaySPI, &CS, &EXTCOM);

You should also swap out the pin names for the relevant names on your platform.

After setup, you usually want to clear any static information left on the screen. To do that, you would call clearImmediate, and optionally provide a callback. The callback will get called when the clearing operation is complete and the display has been cleared. In this example, refreshCallback sets a global boolean 'refreshed' to true when called.

refreshed = false;
int result = display.clearImmediate(refreshCallback);
if(result == LS013B7DH03_OK) {
    while(refreshed == false) sleep();
} else {
    printf("Display error: %d", result);
}

Of course, instead of sleeping while the display is clearing, you could also just continue with the program, and check back whether the callback happened or not.

Then comes the fun part, actually writing stuff on the display! Since the display only supports one-way communication (i.e. you cannot read from it), it uses an internal frame buffer in RAM. So, to actually display something on the LCD, two steps need to happen: writing to the pixel buffer, and at the very end writing the pixel buffer to the LCD.

Pixelbuffer operations

The MemoryLCD library builds upon Simon Ford's TextDisplay library, which means you can use all of that functionality. Even printf is supported!

// Set one pixel at x=10, y=40 to the color White
display.pixel(10,40,White); 

// print "I love mbed" at the character position x=4, y=5
// i.e. starting on row 5, 4 characters from the left border
display.locate(4,5);
display.printf("I love mbed!");

// show a bitmap at a given location
// Constraints: bitmap is 8-bit, MSB first, 1 bit per pixel. Width, height and starting coordinates must be divisible by 8.
// This example: show a bitmap which is 128 pixels wide and high, and start at location 0,0.
display.showBMP(&mbed_logo, 128, 128, 0, 0);

//Draw a line (really a 1px wide rectangle) from (4,10) until (4,15)
display.fill(4, 10, 1, 5, White);

Updating the LCD

Updating the LCD (i.e. moving the framebuffer to the display) happens much the same way as clearing it: asynchronously. To start the update, you call update() on the display, optionally providing a callback to be called after the whole update has happened. In the example below, refreshCallback sets a global boolean 'refreshed' to true when called. Signature: void refreshCallback(void);

refreshed = false;
int result = display.update(refreshCallback);
if(result == LS013B7DH03_OK) {
    while(refreshed == false) sleep();
} else {
    printf("Display error: %d", result);
}

Full example

#include "LS013B7DH03.h"
#include "mbed_logo.h"
/******************** Define I/O *****************************/
DigitalOut myled(LED1);

#define SCK     PD2
#define MOSI 	PD0

DigitalOut CS(PD3);
DigitalOut EXTCOM(PC4);
DigitalOut EXTMODE(PD4);
DigitalOut DISP(PD5);

SPI displaySPI(MOSI, NC, SCK);
silabs::LS013B7DH03 display(&displaySPI, &CS, &EXTCOM);

/******************** Define Timers *****************************/

LowPowerTicker timeKeeping;

/***************** Define global variables **********************/
#define INIT_SECONDS		17600

volatile uint32_t prevSeconds = INIT_SECONDS, seconds = INIT_SECONDS;
volatile bool refreshed = false;

/***************** Define callback handlers *********************/
void secondsCallback(void);
void refreshCallback(void);

void secondsCallback(void) {
	seconds++;
}

/**
 * Callback for refresh completion
 */
void refreshCallback(void) {
	refreshed = true;
}

/*************************** MAIN *******************************/
int main() {
    // Enable the LCD
	EXTMODE = 1;
	DISP = 1;

	// Start generating the 1Hz call for keeping time
	timeKeeping.attach(&secondsCallback, 1.0f);

	// Reset the LCD to a blank state. (All white)
	refreshed = false;
	display.clearImmediate(refreshCallback);
	while(refreshed == false) sleep();

	printf("Initialization done! \n");

	// Apply mbed logo bitmap to the pixel buffer
	display.showBMP((uint8_t*)mbed_enabled_logo, 128, 128, 0, 0);
	display.printf("I like MBED!");

	// Push update to the display
	refreshed = false;
	display.update(refreshCallback);

	// Sleep while doing the transmit
	while(refreshed == false) sleep();

	// Go into clock mode
	while(1) {
		sleep();

		// In clock mode, only update once per second
		if(prevSeconds != seconds) {
			display.locate(4,15);
			display.printf("%02d:%02d:%02d", (seconds / 1200) % 24, (seconds / 60) % 60, seconds % 60);
			if(refreshed == true) {
				prevSeconds = seconds;
				refreshed = false;
				display.update(refreshCallback);
			}
		}
	}
}

Datasheet

Datasheet for the LCD (hosted by Mouser)

/* mbed TextDisplay Library Base Class
 * Copyright (c) 2007-2009 sford
 * Released under the MIT License: http://mbed.org/license/mit
 *
 * A common base class for Text displays
 * To port a new display, derive from this class and implement
 * the constructor (setup the display), character (put a character
 * at a location), rows and columns (number of rows/cols) functions.
 * Everything else (locate, printf, putc, cls) will come for free
 *
 * The model is the display will wrap at the right and bottom, so you can
 * keep writing and will always get valid characters. The location is 
 * maintained internally to the class to make this easy
 */

#ifndef MBED_TEXTDISPLAY_H
#define MBED_TEXTDISPLAY_H

#include "mbed.h"
#include "LCDSettings.h"

class TextDisplay {
public:

  // functions needing implementation in derived implementation class
  /** Create a TextDisplay interface
     *
     * @param name The name used in the path to access the strean through the filesystem
     */
    TextDisplay(const char *name = NULL);

    /** output a character at the given position
     *
     * @param column column where charater must be written
     * @param  row where character must be written
     * @param c the character to be written to the TextDisplay
     */
    virtual void character(int column, int row, int c) = 0;

    /** return number if rows on TextDisplay
     * @result number of rows
     */
    virtual int rows() = 0;

    /** return number if columns on TextDisplay
    * @result number of rows
    */
    virtual int columns() = 0;
    
    // functions that come for free, but can be overwritten

    /** clear screen
    */
    virtual void cls();
    virtual void locate(int column, int row);
    virtual void foreground(uint16_t colour);
    virtual void background(uint16_t colour);
    // putc (from Stream)
    // printf (from Stream)
    virtual void printf(const char* format, ...);
    
protected:

    virtual int _putc(int value);
    virtual int _getc();

    // character location
    uint16_t _column;
    uint16_t _row;

    // colours
    uint16_t _foreground;
    uint16_t _background;
    char *_path;
};

#endif