DOS Serial Monitor

DOS Serial Monitor (SERMON.EXE) is a lightweight, hardware-accelerated MS-DOS serial port monitor designed for debugging a computer's serial port, which uses the RS232 Protocol. It supports translating ANSI and raw hex data. Built entirely from scratch in C++ with the help of Google Gemini for classic MS-DOS environments, it brings a modern, mouse-driven GUI experience into a pure 80x25 text-mode terminal. Like my previous projects, this was built to combine low-level hardware work with a highly polished, retro-futuristic aesthetic. Yes, I know that the whole program is made with the help of AI. Because I'm not good at coding at this level, I only know how to design the user interface.

Screenshots

Main Interface monitoring serial data

Settings Menu with all configurations in tabs

Hex Mode for hardware-level communication

Features

Core Communications Engine

• Direct hardware-level polling bypassing DOS interrupts for maximum speed and stability.
• Support for standard COM ports (COM1 through COM4).
• Adjustable baud rates ranging from 9600 up to 115200 bps.
• Configurable line endings (None, NL, CR, NL/CR) for transmitting data.

Custom VRAM Interface

• Custom graphical window manager running natively in standard DOS 80x25 text mode.
• Highly optimized asynchronous UI engine: interacting with menus, clicking buttons, or using the scrollbar will not block the CPU or drop incoming serial bytes.
• Full mouse support featuring a modern, dynamically resizing scrollbar.
• Shift and drag-click-based text selection and highlighting in the command input buffer.
• Toggleable ANSI and Extended ASCII drawing modes for maximum hardware compatibility.
• Customizable UI themes with adjustable background, foreground, selection, and critical colors.

Hardware Debugging Tools

• HEX Mode: Dynamically translates raw incoming bytes into formatted hex values. When typing in the input box, characters are sent down the serial line as raw hex.
• ANSI Color Parser: Hardware-level parser that reads standard ANSI escape codes to instantly colorize incoming terminal text on the fly.
• Pseudo-Cursor: Software-based block cursor for text input without relying on the BIOS hardware cursor.

Supported Protocols

• Serial Standard: RS-232
• Data Format: 8 Data Bits, No Parity, 1 Stop Bit (8N1)

System Requirements

Recommended For flawless 115200 baud streaming while interacting with the VRAM UI:

• OS: MS-DOS 5.0+, FreeDOS, or modern emulators (DOSBox, DOSBox-X)
• CPU: Intel 80486 DX2-66 or faster (Pentium class recommended for high baud rates)
• RAM: 4 MB
• Video: VGA Compatible Graphics Card
• Input: Microsoft Compatible Mouse (Serial or PS/2) and Standard Keyboard
• Hardware: A physical COM port (UART 16550A with FIFO buffers highly recommended)

Absolute Minimum

• OS: MS-DOS 5.0+
• CPU: Intel 80386
• RAM: 1 MB
• Video: VGA
• Input: Standard Keyboard (Mouse highly recommended for UI navigation)

Tested on

DOS version 7.10 on DOSBox-X version 2025.12.01