🛰️ Garmin 4‑Pin Data/Power Interface Cables
 
(USB Type‑A ↔ Garmin 4‑Pin • DB9 Serial ↔ Garmin 4‑Pin)

Garmin’s early handhelds used a proprietary 4‑pin wide connector. Two official cable types were offered: a USB version for modern PCs and a DB9 serial version for legacy PCs. Both support data transfer and external power.
 
🔧 Cable Forms
USB Cable:
USB Type‑A male ↔ Garmin 4‑pin wide plug
Provides USB‑serial emulation for data + 5V power
Serial Cable:
DB9 male (RS‑232) ↔ Garmin 4‑pin wide plug
Direct RS‑232 signaling, requires COM port on PC
Often used with MapSource/BaseCamp on Windows 95/98/XP
 
🖥️ Compatible Devices
Garmin eTrex series (early models): eTrex (yellow), Venture, Legend (non‑C), Vista (non‑C), Summit, H
Garmin Geko series: Geko 201, Geko 301
Garmin eMap
GolfLogix GPS units (early models built on Garmin hardware)
✅ All devices with the wide 4‑pin port
 
✅ Common Uses
🔄 Data transfer — waypoints, routes, tracks to/from PC
🔋 External power — trickle charging or continuous operation from PC or adapter
🧩 Firmware updates via Garmin software
🧪 Golf course data sync for GolfLogix units
🧵 Legacy GPS maintenance for collectors and retro computing
 
🧠 Signal Format
USB cable: USB 1.1/2.0 host side, emulates COM port via driver
Serial cable: RS‑232 TX/RX/GND direct to DB9 pins
Garmin 4‑pin plug: carries +V, GND, Data In, Data Out
 
⚠️ Things to Watch Out For
📉 Not compatible with newer eTrex models (Legend C, Vista C, eTrex 20/30, Touch) — those use mini‑USB or micro‑USB
🔌 Serial cable requires a real COM port — may need USB‑to‑Serial adapter on modern PCs
 
🛠️ Quick Tips for Beginners
🧭 Check your device’s port: if it has a wide 4‑pin socket, either cable will work
🔌 Use USB cable for modern PCs; use DB9 serial cable for legacy setups
🧪 Install Garmin USB drivers for USB cable; no driver needed for RS‑232
🧯 Keep a spare — these cables are rare but essential for legacy GPS units