servicepoint/about_display.md

About the display

• Resolution: 352x160=56,320 pixels
• Pixels are grouped into 44x20=880 tiles (8x8=64 pixels each)
• Smallest addressable unit: row of pixels inside of a tile (8 pixels = 1 byte)
• The brightness can only be set per tile
• Screen content can be changed using a simple UDP protocol
• Between each row of tiles, there is a gap of around 4 pixels size. This gap changes the aspect ratio of the display.

Binary format

A UDP package sent to the display has a header size of 10 bytes. Each header value has a size of two bytes (unsigned 16 bit integer). Depending on the command, there can be a payload following the header.

To change screen contents, these commands are the most relevant:

1. Clear screen
   • command: 0x0002
   • (rest does not matter)
2. Send CP437 data: render specified text into rectangular region
   • command: 0x0003
   • top left tile x
   • top left tile y
   • width in tiles
   • height in tiles
   • payload: (width in tiles * height in tiles) bytes
     • 1 byte = 1 character
     • each character is rendered into one tile (mono-spaced)
     • characters are encoded using code page 437
3. Send bitmap window: set pixel states for a rectangular region
   • command: 0x0013
   • top left tile x
   • top left pixel y
   • width in tiles
   • height in pixels
   • payload: (width in tiles * height in pixels) bytes
     • network byte order
     • 1 bit = 1 pixel

There are other commands implemented as well, e.g. for changing the brightness.