Keyless Dorm Entry

Step 6 Screen

The screen was recycled from another old device. The protocol for the screen is luckily very common and very well documented. It even has its own Wikipedia page here: http://en.wikipedia.org/wiki/HD44780_Character_LCD. It works similar to the magnetic card reader in that there's a clock pin and data pins. The difference is there are more than one data pins that are used so that entire bytes can be sent at once. Also, communication is only one way; from the microcontroller to the screen. There are a few 'command' bytes and a data bytes. Command bytes are used for things like moving the cursor or clearing the screen. Whether or not a byte is a command is controlled by the R/S or Register Select pin of the LCD. If sending data, the byte is written to the screen where the cursor is and it uses standard ASCII text. I won't go too much into the details of the screen as it's very thoroughly documented elsewhere. For further reading, see http://home.iae.nl/users/pouweha/lcd/lcd.shtml