Display interfaces are crucial for embedded systems, allowing users to interact with devices visually. LCD displays offer versatility, showing text or graphics, while 7-segment displays are simpler but effective for numeric data. Both types have unique interfacing methods and controllers.

Understanding these display options helps engineers choose the right interface for their projects. LCDs use protocols like I2C or SPI, while 7-segment displays can be driven directly or through decoders. Mastering these interfaces enhances the functionality and user experience of embedded systems.

LCD Displays

LCD Controller and Types

• LCD controller interfaces with the microcontroller and drives the LCD display
• Character LCD displays text using a fixed character set stored in the LCD controller (ASCII)
• Graphical LCD displays arbitrary images and graphics by controlling individual pixels
• LCD controllers often have built-in RAM to store display data

Interfacing with LCDs

• I2C interface uses a 2-wire serial communication protocol (SDA and SCL) to control the LCD
• I2C requires fewer microcontroller pins compared to parallel interfaces
• SPI interface uses a 4-wire serial communication protocol (MOSI, MISO, SCK, SS) for faster data transfer
• SPI is generally faster than I2C but requires more microcontroller pins

7-Segment Displays

7-Segment Display Fundamentals

• 7-segment display consists of 7 LED segments arranged in a figure-8 pattern to display numbers and some letters
• Each segment is labeled with a letter (a, b, c, d, e, f, g) for reference
• Common anode displays have a shared positive connection for all segments, while common cathode displays have a shared ground connection
• Segments are illuminated by sinking current through the appropriate segment pins (common anode) or sourcing current to the segment pins (common cathode)

Driving 7-Segment Displays

• BCD (Binary-Coded Decimal) to 7-segment decoder converts a 4-bit BCD input to the corresponding 7-segment display pattern
• BCD to 7-segment decoders simplify the interface between the microcontroller and the display
• Multiplexed display driving allows control of multiple 7-segment displays using fewer microcontroller pins
• In multiplexed driving, the microcontroller rapidly switches between enabling individual displays and updating their segment patterns, taking advantage of human persistence of vision