Interfacing of Seven Segment Display

Introduction

• Today's topic: Interfacing of Seven Segment Display (SSD)
• Previous video covered interfacing of LEDs
• SSD is also referred to as seven segment display device

Basic Concepts

• Two types of LED connections:
  • Common Anode
  • Common Cathode
• Preferred connection for 8051: Common Anode
  • Reason: Common cathode requires minimum 20mA current, which is not possible for 8051
  • Using common anode allows the anode current to flow into the microcontroller

Seven Segment Display Structure

• General structure includes:
  • Segments labeled A to G
  • Decimal point (DP)
  • Anode terminal and cathode terminal
• To display numbers:
  • Example: Displaying 8 means all segments (A-G) should glow, DP off
  • Displaying 1 means only segments B and C should glow
  • Selecting which segments to turn on/off based on desired display

Coding for Seven Segment Display

• Chart for displaying digits 0 to F in hexadecimal:
  • Common Anode configuration:
    • Logic 0 for segments that glow
    • Logic 1 for segments that do not glow
• Example for displaying 8: All segments A to G = 0, DP = 1
• Example for displaying 5: B, E, C segments = 0; others = 1
• Hexadecimal calculation for segments:
  • Example: Displaying 5 corresponds to binary representation

Interfacing Multiplexed Display

• Requirement for using 4 SSDs
  • Connecting one SSD to one port requires four ports (P0 to P3)
  • Can create a multiplexed display to reduce the number of ports used
  • Activate one display at a time to simulate all displays working simultaneously

Interfacing Diagram

• Block diagram includes:
  • PNP transistors connected to four SSDs
  • Current limiting resistors for each segment
  • Requirements for logic levels to activate the desired SSD
• Logic levels:
  • Activate one transistor by applying logic 0 to its base, others at logic 1
  • Example: Pin P2.0 activated while others are not

Programming

• Discussed a programming example using embedded C
  • Assume a delay of 10 milliseconds
• Basic delay calculation:
  • T_in = 1.085 microseconds
  • Calculate N for required delay
• Example hex counter program:
  • Counting from 0 to 15 in hexadecimal
  • Display logic and delay functions

Interfacing Diagram

• Interfacing diagram includes:
  • Port connections
  • Display driver (74LS424)
  • Corresponding segments

Conclusion

• Summarized the interfacing of SSD with 8051 microcontroller
• Discussed relevant programming details and calculations
• Reminder to draw the interfacing diagram and write the program
• Thanked students for watching the session.