microprocessor 8085

🧠 8085 Microprocessor Development Kit

This project is a full schematic of an 8085-based microprocessor system, built using EasyEDA. It includes a working setup with memory, address decoding, IO ports, and timing circuitry — designed as an educational kit or foundation for further expansion (e.g., display, keypad, or other peripherals).

🔧 Features

• 8085 CPU (U1)
  Central processor that drives instruction execution.

• 2732 EPROM (U3)
  Used for storing permanent programs/code. Address decoding enables program memory mapping.

• HM6116 SRAM (U4)
  2K RAM chip for general data storage.

• 74LS373 (U5)
  Latch used to separate multiplexed address/data bus from 8085.

• 74LS138 (U6)
  3-to-8 decoder for address decoding: selects ROM, RAM, and Port space.

• 8155 (or External Ports - P1, P3, P4)
  Provides I/O lines for user interaction or peripherals.

• CD4040 (U7)
  Binary counter, used here to generate timing pulses or signals.

• LM7805 (U8)
  Power regulation: provides +5V supply to the circuit.

• XTAL + Capacitors
  Provides 6.144 MHz clock frequency to the CPU for stable operation.

🗺️ Block Diagram Overview

    +---------+     +----------+     +---------+
    |         |     |          |     |         |
    |  8085   +---> |  Latch   +---> | Address |
    |         |     |  74LS373 |     |  Lines  |
    +----+----+     +----+-----+     +----+----+
         |               |                |
         |               |                |
         v               v                v
     Multiplexed     Control         Decoder (74LS138)
     AD0–AD7 Bus     Signals          /    |    \
                                     ROM  RAM  IO Ports

⚙️ Schematic

The full schematic is built in EasyEDA and includes:

• All IC connections

• Power routing

• Control signals (RD, WR, IO/M, ALE, RESET, INT, etc.)

• Address & data bus routing

• Decoder enable logic

• Program storage in ROM

• RAM for data

🖼️ Preview available in repository:

📄microprocessor dev kit

🛠️ To-Do (Future Improvements)

• Add 7-Segment display or LCD output

• Integrate 8255 or 8155 for IO control

• Add keypad input interface

• Program and burn HEX code to EPROM

• Design PCB layout based on schematic

❌ Why Simulation Doesn't Work

EasyEDA does not support microprocessor simulation for full systems. The schematic is meant for:

• PCB manufacturing

• Reference

• Educational design

If you want to simulate logic or partial sections:

• Use Logisim for logic gates and decoder testing

• Use Proteus for full 8085 CPU-level simulation (commercial)

📜 License

MIT License – Feel free to use, modify, or build upon this project. Give credit where due! 👍