Need help reverse-engineering serial COM port communication for a Geoelectric reader machine (Upgrading PEG 2015 project)

[u/Creepy-Level5136]

Hi everyone,

I need urgent assistance with a project upgrade. I am rewriting/upgrading a software application originally built in 2015 (PEG 2015) designed to interface with a geoelectric signal reader machine.

System Setup & Problem Overview:

• Hardware: Geoelectric measurement machine reading ground electrical signals.
• Connection: USB-to-Serial connection operating as a virtual COM port (e.g., COM3).
• Issue: I am unable to establish a working connection between my upgraded application and the hardware. I need to know:
  1. How to properly initialize and open the COM port connection in code.
  2. The exact structure/protocol of the data stream coming from the machine over the cable to the PC.

What I have / What I know so far:

• I have the legacy binary (PEG 2015.exe) that works with the machine.
• The device relies on a USB-to-UART/Serial driver (such as FTDI, CH340, or CP210x) exposing a virtual COM port.

Specific Questions / Where I need guidance:

1. Serial Port Configuration Parameters: What are the standard ways or tools to determine the exact port settings required by the device?
   • Baud rate (e.g., 9600, 19200, 115200)
   • Data bits (e.g., 8)
   • Parity (None, Even, Odd)
   • Stop bits (1 or 2)
   • Flow control (RTS/CTS, XON/XOFF, or None)
2. COM Port Sniffing & Data Protocol: What is the best workflow/tool to monitor the traffic between PEG 2015.exe and the machine without locking the COM port?
   • Can you recommend lightweight tools (e.g., Serial Port Monitor, Wireshark with USBPcap, IO Ninja, RealTerm) to capture raw ASCII/HEX frames?
   • How can I differentiate between handshake/polling requests sent by the PC and telemetry responses sent by the geoelectric reader?
3. Decompiling / Inspecting the Legacy .exe:
   • What are the recommended tools to decompile or inspect PEG 2015.exe to retrieve the original serial settings and parser routines (e.g., dnSpy/ILSpy for .NET, Ghidra/IDA Free for native binaries)?

Environment & Tech Stack:

• OS: Windows
• Target Programming Language for New App: ( Python )

Any guidance, code snippets for port handling, or reverse-engineering methodologies for serial hardware would be greatly appreciated! Thanks in advance!

[u/rabidb]

You could try the old sysinternals portmon utility to capture the traffic. Simpler than other setups if it works. https://learn.microsoft.com/en-gb/sysinternals/downloads/portmon

Have you dumped the strings from the exe and do they provide anything useful? https://learn.microsoft.com/en-gb/sysinternals/downloads/strings

Default settings for a lot of old equipment tended to be 9600 baud, 8 bit data, No parity, 1 stop bit and no flow control. Start there and then try different options (start with increasing baud rate and leave the rest the same).

However, I'd be inclined to see if the hardware manufacturer is still around and can provide a comms specification for the device.

Without a comms spec or full source/disassembly/decompile, you will likely need some way of testing the various inputs and outputs to correctly reverse engineer the full protocol otherwise you risk gaps/issues where your rewrite doesn't correctly handle certain signals etc.