vrEmuLcd - HD44780 Character LCD Emulator

Core engine written in C with a flexible Web front-end.

This Character LCD Emulator can be used to emulate most standard LCD displays.

It accepts and responds to most commands listed in the HD44780 datasheet

It also now support most commands for a 128x64 graphics LCD 12864B datasheet

Screenshots:

Hello, World!

Different Colors

Different Sizes

128 x 64 Graphics LCD

Custom characters (CGRAM support)

Live examples:

• Hello, World!
• The 8-Bit Guy: Character LCD
• Hello Graphics LCD
• Troy’s Breadboard Computer!

Usage

C

#define LCD_WIDTH 20
#define LCD_HEIGHT 4

VrEmuLcd      *lcd = vrEmuLcdNew(LCD_WIDTH, LCD_HEIGHT, EmuLcdRomA00);

// send it commands:
vrEmuLcdSendCommand(lcd, LCD_CMD_FUNCTION | LCD_CMD_FUNCTION_LCD_2LINE | 0x10);
vrEmuLcdSendCommand(lcd, LCD_CMD_CLEAR);
vrEmuLcdSendCommand(lcd, LCD_CMD_HOME);
vrEmuLcdSendCommand(lcd, LCD_CMD_DISPLAY | LCD_CMD_DISPLAY_ON);

// send it data
vrEmuLcdWriteByte(lcd, 'H');
vrEmuLcdWriteByte(lcd, 'e');
vrEmuLcdWriteByte(lcd, 'l');
vrEmuLcdWriteByte(lcd, 'l');
vrEmuLcdWriteByte(lcd, 'o');

// or cheat
vrEmuLcdWriteString(lcd, " world!");

// then periodically, render it. 
vrEmuLcdUpdatePixels(lcd);   // generates a snapshot of the pixels state

for (int y = 0; y < vrEmuLcdNumPixelsY(lcd); ++y) {
  for (int x = 0; x < vrEmuLcdNumPixelsX(lcd); ++x) {
    // do whatever you like with the pixel information. render it to a texture, output it to  a console, whatever
   // values returned are:  -1 = no pixel (character borders), 0 = pixel off, 1 = pixel on
    char pixel = vrEmuLcdPixelState(lcd, x, y);
  }
}

Web

HTML (local)

<script src="src/vrEmuLcd.js"></script>
<script src="bin/vrEmuLcdWasm.js"></script>

HTML (live)

<script src="https://visrealm.github.io/vrEmuLcd/src/vrEmuLcd.js"></script>
<script src="https://visrealm.github.io/vrEmuLcd/bin/vrEmuLcdWasm.js"></script>

Example

<canvas id="lcd"></canvas>
...
<script>
    var canv = document.getElementById('lcd');
    var ctx = canv.getContext('2d');

    vrEmuLcd.setLoadedCallback(function () {

      // create a new LCD object
      var lcd = vrEmuLcd.newLCD(16, 2, vrEmuLcd.CharacterRom.Eurpoean);

      // set up the display
      lcd.sendCommand(LCD_CMD_DISPLAY | LCD_CMD_DISPLAY_ON);

      lcd.writeString("Hello, World!");

      lcd.render(ctx, 0, 0, 800, 400);
    });
</script>

LCD API

constuctor

var lcd = vrEmuLcd.newLCD(columns, rows, charSet);

• columns: - number of columns
• rows: - number of rows
• charSet: - character set. One of: vrEmuLcd.CharacterRom.European, vrEmuLcd.CharacterRom.Japanese

sendCommand(commandByte)

Send a command to the instruction register of the lcd Command constants are defined:

• LCD_CMD_CLEAR - clear the display

• LCD_CMD_HOME - reset display to home position

• LCD_CMD_ENTRY_MODE - entry mode (the following to be bitwise-OR’d)
  • LCD_CMD_ENTRY_MODE_INCREMENT - automatically increment the cursor or display
  • LCD_CMD_ENTRY_MODE_DECREMENT - automatically decrement the cursor or display
  • LCD_CMD_ENTRY_MODE_SHIFT - automaticallt shift the entire display instead of the cursor
• LCD_CMD_DISPLAY - display mode (the following to be bitwise-OR’d)
  • LCD_CMD_DISPLAY_ON - turn the display on
  • LCD_CMD_DISPLAY_CURSOR - display a cursor (bottom row)
  • LCD_CMD_DISPLAY_CURSOR_BLINK - display a blink cursor (flashing entire character block)
• LCD_CMD_SHIFT - move the cursor or scroll display (the following to be bitwise-OR’d)
  • LCD_CMD_SHIFT_CURSOR - shift the cursor (default)
  • LCD_CMD_SHIFT_DISPLAY - shift the display
  • LCD_CMD_SHIFT_LEFT - shift the cursor or display left (default)
  • LCD_CMD_SHIFT_RIGHT - shift the cursor or display right

• LCD_CMD_SET_CGRAM_ADDR - set the CGRAM address (actual address uses lower 6 bits)

• LCD_CMD_SET_DRAM_ADDR - set the CGRAM address (actual address uses lower 7 bits)

writeByte(dataByte)

Write a byte to the data register of the lcd

writeString(str)

Write a string to the data register of the lcd

getDataOffset(screenX, screenY)

Return the ddram offset for the given screen location

readByte()

Read the current byte from cgram or ddram (determined by current address)

readAddress()

Read the current address offset in cgram or ddram

pixelState(pixelX, pixelY)

Return the pixel state at the given location

• -1 - no pixel (eg. margin)
• 0 - pixel off
• 1 - pixel on

colorScheme

Set/get the color scheme. eg:

lcd.colorScheme = vrEmuLcd.Schemes.WhiteOnBlue;

Standard color schemes:

• vrEmuLcd.Schemes.WhiteOnBlue (default)
• vrEmuLcd.Schemes.BlackOnBlue
• vrEmuLcd.Schemes.BlackOnGreen
• vrEmuLcd.Schemes.RedOnBlack
• vrEmuLcd.Schemes.BlueOnBlack

or, provide your own. { BackColor: <backcolor>, PixelOnColor: <pixeloncolor>, PixelOffColor: <pixeloffcolor> }

render(ctx, x, y, width, height)

Render to a 2d canvas context

• ctx - the canvas to render to

License

This code is licensed under the MIT license