8086 Microprocessor-Based Keypad Authentication System with LED Display & Buzzer

This project implements a simple authentication and LED pattern display system using an 8086 microprocessor, interfaced with a 4x3 keypad, LEDs, and a buzzer. The system authenticates a user-entered password and, upon success, allows selection of LED display patterns.

Start → Init 8255 → Enter PIN → [Correct?]
                                    │
                      ┌──── No ─────┐  ──── yes ─────┐
                      ▼             ▼                ▼
                  Buzzer ON       Retry            Pattern
                                  Auth             Choice 
                                                      ▼
                                                 Keypad Input → Run Pattern → Loop

Main Hardware Components

• 8086 Microprocessor [U1]: Core CPU controlling the system flow.

• 8255 Programmable Peripheral Interface (PPI) [U8]: Used to interface with keypad, LEDs and buzzer.

• 74LS373 Octal Transparent Latch [U2, U3, U4]: To isolate the address bits permanently for decoding or interfacing.

  • LE (Latch Enable): Connected to ALE from 8086
  • OE (Output Enable): Grounded

• 74LS138 3-to-8 Line Decoder [U7]: To decode address lines and generate chip select (CS) signals for the 8255 PPI (U8).

  Port selection happens with A1 and A2 with PortA starting address calculated by bitmasking the last 2 digits of the university ID:

  0100 1001 & 1111 1000 = 0100 1000 (48H) 
  

  Resulting in the port addresses (48H, 4AH, 4CH, 4EH). The remaining bits are used for the chip select.

  • Inputs A, B and C receive address lines A3, A4 and A6, enabling 8255 on 101
  • Inputs E2 and E3 receive address lines A5 and A7

• 74LS245 Octal Bus Transceiver [U5, U6]: To buffer or isolate data buses from peripherals for timing or voltage protection.

  • U5 connects the lower data bus (D0–D7)
  • U6 connects the upper data bus (D8–D15)

Software Components

Written for 8086 architecture with password authentication (8-6-4-9) and four different LED patterns (Left to Right, Alternating, Counting, Ping-Pong) and buzzer feedback for incorrect password attempts. Data segment initialization is as follows:

DATA SEGMENT
    portA     EQU 48H     ; LEDs (PA0-PA7)
    portB     EQU 4AH     ; Keypad rows (PB0-PB3)
    portC     EQU 4CH     ; Keypad cols (PC0-PC3) + Buzzer (PC7)
    CWR       EQU 4EH     ; 8255 Control Register

    pswd      DB 8,6,4,9
    buzzer    DB 0        ; 00h = off, 80h = on
    buffer    DB 4 DUP (0)
DATA ENDS

The assembly source code includes explicit routines for initialization, keypad scanning, authentication and LED patterns.

Pattern 1: Left to Right Shift

AL = 00000001b → 00000010b → ... → 10000000b

Pattern 2: Alternating Blink

AL = 01010101b → 10101010b → repeat 8 times

Pattern 3: Binary Counter

AL = 00000000b to 11111111b (0 to 255)

Pattern 6: Ping-Pong

AL = 00000001b → shift left to 10000000b → then shift back to 00000001b → repeat

This project includes a software-controlled buzzer for safe I/O handling, a modular 8086 assembly design with distinct processes for every LED pattern, and appropriate stack usage to maintain register state. After successful authentication, it continuously loops a few chosen LED patterns and features dependable keypad input with software debounce.