add information about display hardware

README.md

@@ -21,6 +21,50 @@ Take a look at the contained crates for language specific information:
 
 To add yourself to the list, open a pull request.
 
+## 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.
+
+The commands are implemented in DisplayCommands.
+
+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.
+
+
 ## Where is servicepoint1?
 
 This library is a spiritual mix of a not-yet-working rust library called `servicepoint` and a bunch of working but also