8085 BIOS System - Interactive Development Environment

A complete 8085 microprocessor system with integrated BIOS/monitor ROM and interactive GUI. Perfect for learning 8085 programming, developing operating systems, or testing embedded software.

Features

BIOS Monitor ROM

• Reset initialization with banner
• Interactive command prompt with basic commands:
  • H: Help - display available commands
  • D addr len: Dump memory in hex format
  • M addr: Modify memory bytes interactively
  • G addr: Jump to address and execute
  • L: Load Intel HEX programs into memory
• Console I/O via I/O ports 0 (input) and 1 (output)

Emulator Features

• Complete 8085 instruction set (all 246 valid opcodes)
• Interactive Terminal - Type commands directly into the BIOS
• Real-time Register Display - Watch A, B, C, D, E, H, L, SP, PC
• Flags Display - Monitor S, Z, AC, P, CY flags
• Memory Viewer - See first 256 bytes of memory
• Step/Run/Stop Controls - Debug or run programs
• Load Programs - Load binary files for testing
• GUI built with Qt5 - Modern, responsive interface

Architecture

The system integrates:

• C++ 8085 Emulator (cpu8085.cpp) - Full instruction set with I/O callbacks
• BIOS Monitor (src/bios.asm) - Assembled to build/bios.bin, loaded at 0x0000
• Qt5 GUI (bios_gui.cpp) - Interactive terminal and system controls
• I/O Port System - Port 0 (console in), Port 1 (console out)

This is written in C++17 with Qt5 for the GUI, and 8080/8085-compatible assembly (using Macroassembler AS asl) for the BIOS.

Assumptions and I/O contract

By default, the monitor uses two I/O ports for console:

• IN from port 0: returns the next ASCII byte if available; returns 0 if no character. The monitor busy-waits until non-zero.
• OUT to port 1: write an ASCII byte to the console output.

You can change these ports at the top of src/bios.asm by editing the equates CONIN_PORT and CONOUT_PORT.

If your emulator has different semantics (e.g., separate status ports), you can adapt the con_getc and con_putc routines accordingly.

Layout

• src/bios.asm — Monitor BIOS source, ORG 0x0000
• Makefile — Build targets for .bin and .hex
• tools/assemble.sh — Helper script to assemble with asl

Prerequisites

Required

• Qt5 development libraries:

  sudo dnf install qt5-qtbase-devel  # Fedora
  # or
  sudo apt-get install qtbase5-dev   # Ubuntu/Debian

• C++ compiler (g++ 7+ or clang++)

Optional (for building BIOS from source)

• Macroassembler AS (asl) and its p2bin/p2hex tools

  On Fedora/RHEL:

  sudo dnf install asl

  On Debian/Ubuntu (may need to build from source):

  sudo apt-get install -y build-essential bison flex
  git clone https://github.com/alfako/asl.git
  cd asl
  make
  sudo make install

Build

Quick Build (using Make)

cd /home/kde/Documents/8085_bios
make quick

This builds:

• build/bios.bin — BIOS ROM (assembled from src/bios.asm)
• 8085_bios_system — Qt GUI emulator executable

Alternative: CMake Build

mkdir build && cd build
cmake ..
make

Run

./8085_bios_system

or

make run

Usage

1. Launch the emulator - The GUI will open with an interactive terminal
2. Click "Load BIOS" - Loads build/bios.bin into memory at 0x0000
3. Click "Run" - The 8085 starts executing from 0x0000
4. See the BIOS banner in the terminal
5. Type commands at the > prompt (try H for help)
6. Use BIOS commands to dump memory, modify bytes, or load programs

Clean

make clean

BIOS Command Examples

When the BIOS monitor prompt (>) appears, you can use these commands:

• H - Display help
• D 2000 40 - Dump 64 (0x40) bytes from address 0x2000
• M 2100 - Modify bytes at address 0x2100
  • Enter hex bytes like 3E C3 00 10
  • Press . or Enter on blank line to finish
• G 1000 - Jump to address 0x1000 and execute
• L - Load Intel HEX format program
  • Paste Intel HEX records into terminal
  • Loader auto-detects EOF record

Notes:

• Hex numbers are case-insensitive
• Whitespace between hex digits is flexible
• HEX loader supports record types 00 (data) and 01 (EOF)

Developing Your Own Programs/OS

Method 1: Write Assembly & Load

1. Write your program in 8085 assembly (e.g., myprogram.asm)
2. Assemble it with your preferred assembler (asl, as85, etc.)
3. Use BIOS L command to load Intel HEX
4. Use BIOS G command to execute

Method 2: Direct Binary Load

1. Write program in assembly, assemble to .bin
2. Click "Load Program..." in the GUI
3. Program loads at 0x2000 by default
4. Use BIOS command G 2000 to execute

Method 3: Extend the BIOS

Edit src/bios.asm to add:

• New monitor commands
• Device drivers
• System calls for your OS
• Boot loader logic

Then rebuild and test!

I/O Port Configuration

The BIOS uses these I/O ports (configurable in src/bios.asm):

• Port 0 (IN): Console input - returns ASCII character or 0 if no key pressed
• Port 1 (OUT): Console output - sends ASCII character to terminal

To add more I/O devices:

• Define new port numbers in your program
• Use IN port / OUT port instructions
• Extend cpu8085.cpp I/O callbacks if needed for special hardware simulation

Project Structure

custom_8085_system/
├── src/
│   ├── bios.asm          # Monitor BIOS source code
│   ├── os_multitask.asm  # OS with shell + multitasking (Phase A+C)
│   ├── os_shell.asm      # OS shell (Phase A standalone)
│   ├── os_v03.asm        # OS version 0.3
│   └── scheduler.asm     # Task scheduler (Phase C standalone)
├── tools/
│   ├── assemble.py       # Python assembler wrapper
│   └── assemble.sh       # Shell assembler script
├── build/                # Created during build process
│   ├── bios.bin          # Assembled BIOS ROM
│   └── bios.hex          # Intel HEX format
├── cpu8085.h             # 8085 emulator core header
├── cpu8085.cpp           # 8085 emulator implementation
├── bios_gui.cpp          # Qt5 GUI with interactive terminal
├── CMakeLists.txt        # CMake build configuration
├── test_minimal.asm      # Minimal test assembly file
└── README.md             # This file

Troubleshooting

• BIOS doesn't load: Make sure build/bios.bin exists (run make first)
• No terminal output: Check that BIOS is loaded and you clicked "Run"
• Keyboard not working: Terminal widget should have focus; click in the terminal area
• Assembler errors: Check build/bios.lst for assembly errors
• Emulator won't build: Ensure Qt5 development packages are installed

Future OS Development

This system provides everything needed to develop a simple operating system:

1. BIOS provides: Console I/O, memory management primitives, program loader
2. You can add: File system, process scheduling, interrupt handlers
3. Extend with: More I/O devices, disk simulation, network simulation
4. Test immediately: No need for real hardware!

License

A permissive license similar to the BSD 2-Clause License, but with a 3rd clause that prohibits others from using the name of the copyright holder or its contributors to promote derived products without written consent.