Get Started with your SFP-to-TTL Adapter

Get Started with your SFP-to-TTL Adapter
Photo by Braden Collum on Unsplash

You scanned the QR code on the board — welcome. This page gets you from "just opened the envelope" to "reading the serial console", and points you to the deeper guides when you need them.

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Read this first: the board's headers are labelled for the typical GPON/XGS-PON stick, but pinout, baud rate, parity and voltage can differ from one module to the next. Do not wire anything until you've looked up the parameters for your exact stick. Wrong pin or wrong voltage can kill the module.

Step 1 — Find the parameters for YOUR module (do this before touching a wire)

Every stick is a little different. Before you connect anything, look up your exact module and note down:

  • Which SFP pins carry the console (TX / RX). Most sticks use pins 2 & 7 — that's what the board's labels assume — but not all, so confirm it.
  • Baud rate (commonly 115200, sometimes 9600 or other).
  • Parity / frame (usually 8N1 — confirm).
  • Logic voltage — GPON UART is normally 3.3 V. Confirm it and use a 3.3 V cable; 5 V can destroy the stick.

Where to look it up:

Golden rule: you don't plug in until you know how to plug in.

Step 2 — What this board does

It's a passive breakout: an SFP connector that exposes the 20 pins of a fibre stick on 2.54 mm headers labelled on the silkscreen — no soldering. It gives you access to the UART serial console of a GPON / XGS-PON module so you can flash firmware, bypass the operator ONT, or read the bootloader logs.

It does not power the stick and does not convert logic levels — you bring your own USB-TTL cable at the voltage your stick expects (see Step 1).

Step 3 — What you need

  • Your GPON / XGS-PON SFP stick, with its parameters looked up (Step 1).
  • A USB-to-TTL / UART cable (FTDI, CP2102, CH340…) at your stick's logic voltage — almost always 3.3 V, never 5 V.
  • A 3.3 V power source for the stick, wired to the board's VCC and GND headers. This can be your USB-TTL cable's 3.3 V line, or a separate bench supply. The board carries power through to the stick — it doesn't generate it.
  • A terminal: screen, minicom, PuTTY, or your tool of choice.

Step 4 — Wiring

Using the pins you confirmed in Step 1:

  1. Slide the stick fully into the SFP connector on the board.
  2. Wire the serial lines between your USB-TTL cable and the labelled headers (cross them over):
    • cable RX → board TX>RX
    • cable TX → board RX>TX
  3. Power the stick through the board's power headers:This is what turns the stick on — the board doesn't power it by itself.
    • 3.3 V → board VCC
    • GND → board GND (shared with the serial ground above)

Open your terminal with your stick's baud rate and frame (e.g. 115200 8N1), no flow control:

screen /dev/ttyUSB0 115200

Apply power — boot logs should scroll immediately.

Seeing nothing? Swap RX/TX — the single most common mistake. Still nothing → re-check the baud rate and voltage against Step 1.

Step 5 — Flashing & firmware

Once you have a console:

Step 6 — Configuring your ISP box

Replacing your operator's ONT with a flashed stick means matching your ISP's GPON parameters (serial number / GPON SN, PLOAM password, VLAN, sometimes S/N spoofing). These are ISP-specific — hack-gpon.org documents the settings for most European operators, and the 8311 community forum covers the rest.

🇫🇷 French-speaking users: the lafibre.info forum is the go-to community for per-operator GPON settings (Orange, Free, SFR, Bouygues…), alongside the reference wiki hack-gpon.org.

⚠️ Bypassing your operator's ONT can breach your subscription terms and, if misconfigured, disturb the PON for other subscribers on your street. Know your ISP's rules and your local regulations before you go live.

Troubleshooting

  • Stick keeps rebooting? Nine times out of ten it's the power supply, not the stick — read: why your SFP module keeps rebooting.
  • Garbage on the console? Wrong baud rate — re-check Step 1.
  • Nothing at all? RX/TX swapped, wrong pins, or the cable is the wrong voltage.