FIS-Display

VW Passat B6 FIS/MFA Display — Hardware Connections and Software Protocols.

Disclaimer

The creator takes no responsibility for damages, immobile car, injury, or any other loss arising from the use of this project, its firmware, PCB design, or documentation. Use at your own risk.

What this project does

Navit is an open-source, modular turn-by-turn navigation engine that can run on Linux, Android, and other platforms. This project uses Navit on a host device (with D-Bus enabled) to drive the car's FIS/MFA display.

This repository provides firmware, PCB design, and documentation to show Navit navigation (and optionally media, call, clock) on the VW Passat B6 (3C) FIS/MFA display. A host device runs Navit with D-Bus and sends a simple serial protocol to a Raspberry Pi Pico 2 W over USB or Bluetooth (pair once as FIS-Bridge). The Pico injects frames onto the car's 3LB bus during idle gaps so the cluster shows turn-by-turn directions, street name, distance, and maneuver icons; when not navigating, it can show media track info, incoming call caller ID, or a clock screen with GPS time, ETA (e.g. ARR 14:32), remaining distance, and compass heading. Optional CAN bus support (MCP2561, disabled by default) is included when the firmware functions for that is finished. The Pico is a middleman only; all navigation logic stays on the host. When CAN bus is enabled, it can adjust your clock automatically. A separate display-test firmware is provided for bench-testing the cluster without a Navit host.

PCB and schematic are designed in KiCad. Design files and Gerbers are in pcb-files/. See Gerber files and PCB manufacturing for what they are and how to use them.

Note: The firmware in firmware/ is experimental and untested on a real vehicle. Validate on the bench before connecting to the car. See firmware/README.md for build and flash instructions.

Gerber files and PCB manufacturing

What are Gerber files? Gerber is the standard format used by PCB manufacturers to produce printed circuit boards. Each file describes one layer of the board (copper, solder mask, silkscreen, etc.) as vector graphics. The manufacturer combines these files to fabricate and assemble the PCB. This repository provides Gerbers exported from the KiCad project in pcb-files/FIS-display/.

What is in this repo: In pcb-files/FIS-display/gerbers/ you will find:

• Copper layers: F_Cu.gbr (top copper), B_Cu.gbr (bottom copper)
• Solder mask: F_Mask.gbr, B_Mask.gbr
• Silkscreen: F_Silkscreen.gbr, B_Silkscreen.gbr
• Solder paste (SMD stencil): F_Paste.gbr, B_Paste.gbr
• Board outline: Edge_Cuts.gbr
• Drill files: *.drl (through-hole and non-plated drill data)

How to use them:

1. Ordering PCBs: Zip the contents of the gerbers/ folder (all .gbr and .drl files, and the .gbrjob file if the manufacturer supports it) and upload the zip to a PCB fab (e.g. JLCPCB, PCBWay, OSH Park, or similar). Select the correct units (usually mm) and board thickness; the fab will use the Gerbers to produce the boards. Use the same BOM as in firmware/BOM.md for sourcing components.

2. Viewing without KiCad: You can inspect the layers with a Gerber viewer (e.g. GerberView, or the online viewer many fabs provide) to check traces, pads, and outline before ordering.

3. Editing the design: Open the KiCad project in pcb-files/FIS-display/ (.kicad_pro, .kicad_sch, .kicad_pcb) in KiCad. After any change, re-export Gerbers from KiCad (File → Plot, then generate drill files) and replace the files in gerbers/ before ordering new boards.

Table of contents

• Disclaimer
• What this project does
• Gerber files and PCB manufacturing
• Project structure
• 1. System Overview
• 2. Host Device — Navit with D-Bus
  • 2.1 Supported Platforms
  • 2.2 D-Bus Service Details
  • 2.3 Key Attributes to Subscribe To
  • 2.4 Navigation Status Values
  • 2.5 D-Bus Listener to Pico Bridge Script
• 3. Serial Protocol (Host to Pico, 115200 baud)
• 4. Transport — USB CDC or Bluetooth SPP
  • USB CDC
  • Bluetooth SPP
• 5. Hardware
  • 5.1 Controller — Raspberry Pi Pico 2 W
  • 5.2 The 3LB (Three-Line Bus)
  • 5.3 Level Shifting
  • 5.4 Instrument Cluster Connector (Green T32a)
  • 5.5 Inline PCB Connector
  • 5.6 Pico 2 W GPIO Pinout
  • 5.7 Cluster Coding Prerequisite
• 6. The 3LB Protocol
  • 6.1 Open Source Libraries (Reference)
  • 6.2 Display
  • 6.3 OEM radio: CAN time and display (reference only)
  • 6.4 Other potentially useful CAN messages (reference only)
• 7. Firmware Runtime Behaviour
• 8. Software Stack Summary
• 9. Key References

Project structure

This repository uses no symlinks; all paths are normal directories and files so that every system can clone and use it without symlink support.

1. System Overview

┌──────────────────────────────────────────────────────────┐
│  Host device running Navit with D-Bus enabled            │
│                                                          │
│  Examples:                                               │
│  • Android head unit (Navit built with D-Bus support)    │
│  • Linux carputer / Raspberry Pi running Navit           │
│  • Any platform where libbinding_dbus.so is active       │
│                                                          │
│  D-Bus listener translates Navit signals to serial       │
│  protocol and forwards to Pico over USB or Bluetooth     │
└────────────┬─────────────────────────┬───────────────────┘
             │                         │
     USB CDC serial            Bluetooth SPP
     /dev/ttyACM0              (onboard CYW43439)
     (also powers Pico)        "FIS-Bridge" PIN 0000
             │                         │
             └──────────┬──────────────┘
                        │
               ┌────────▼─────────┐
               │ Raspberry Pi     │
               │ Pico 2 W         │
               │ (RP2350)         │
               │                  │
               │ Middleman:       │
               │ serial -> 3LB;   │
               │ optional: GPIO   │
               │ 11/12 -> MCP2561 │
               └────────┬─────────┘
                        │
         ┌──────────────┼──────────────┐
         │              │              │
         ▼              │              ▼
 3LB (ENA/CLK/DATA)     │      Optional CAN (if enabled):
 via BS170 level        │      GPIO 11 (TX), 12 (RX) ->
 shifters (3.3V<->5V)   │      MCP2561 (TXD/RXD) -> CAN-H/CAN-L
         │              │              │
         ▼              │              ▼
 ┌──────────────────┐   │   ┌──────────────────────────┐
 │ VW Passat B6 (3C) │   │   │ Comfort/infotainment CAN  │
 │ FIS/MFA cluster   │◄──┘   │ 100 kbit/s (when fitted) │
 │ 64x88 px, 1-bit   │       └──────────────────────────┘
 └────────┬──────────┘
          │
          ▼
 ┌───────────────────────┐
 │ Original ECU          │
 │ (talks 3LB natively,  │
 │  Pico co-exists via   │
 │  ENA arbitration)     │
 └───────────────────────┘

The Pico 2 W is a pure middleman. It has no navigation intelligence — it only receives
the serial protocol from the host device and injects the translated frames onto the 3LB bus.
All navigation logic stays on the host device running Navit. Optionally, when CAN is enabled
(see 5.6 Pico 2 W GPIO Pinout), the Pico can communicate with the
vehicle comfort/infotainment CAN (100 kbit/s) via GPIO 11/12 to the MCP2561 (TXD/RXD only).

The original ECU continues to talk to the FIS/MFA natively over 3LB at all times. The Pico
co-exists on the bus using the ENA line for arbitration — no relay or analog switch is needed.

Note: The OEM radio has been replaced with an aftermarket head unit. The head unit does
not communicate over 3LB. Only the original ECU talks to the FIS/MFA natively over 3LB.

2. Host Device — Navit with D-Bus

2.1 Supported Platforms

Navit can be built with D-Bus support (libbinding_dbus.so) on multiple platforms:

Enable D-Bus in navit.xml:

<plugin path="$NAVIT_LIBDIR/*/${NAVIT_LIBPREFIX}libbinding_dbus.so" active="yes"/>

2.2 D-Bus Service Details

2.3 Key Attributes to Subscribe To

2.4 Navigation Status Values

2.5 D-Bus Listener → Pico Bridge Script

This script runs on the host device and forwards Navit D-Bus signals to the Pico over either
USB CDC or Bluetooth SPP. Configure SERIAL_PORT to match your transport:

• USB CDC: typically /dev/ttyACM0 (Linux/Android)
• Bluetooth SPP: the rfcomm device created when paired to FIS-Bridge, e.g. /dev/rfcomm0

#!/usr/bin/env python3
"""
Navit D-Bus listener -> Pico 2 W serial bridge.
Runs on any platform where Navit is built with libbinding_dbus.so active:
Android (with D-Bus support), Linux carputer, Raspberry Pi, etc.
Transport: USB CDC or Bluetooth SPP -- configure SERIAL_PORT below.
"""

import serial
import dbus
import dbus.mainloop.glib
from gi.repository import GLib

SERIAL_PORT = "/dev/ttyACM0"   # USB CDC, or e.g. /dev/rfcomm0 for Bluetooth SPP
BAUD = 115200

WATCHED = [
    "navigation_next_turn",
    "navigation_distance_turn",
    "navigation_street_name",
    "navigation_status",
    "eta",
    "destination_length",      # remaining distance (m) -> NAV:REMAIN, shown on FIS clock line
    "position_direction",      # heading 0-360 -> NAV:HEAD, shown as compass (N, NE, E, ...)
    "position_time_iso8601",   # UTC GPS time for FIS clock (format YYYY-MM-DDTHH:MM:SSZ)
    "position_coord_geo",      # lat/lon for timezone lookup (vehicle attribute)
]

MANEUVER_MAP = {
    "straight":          "straight",
    "turn_left":         "turn_left",
    "turn_right":        "turn_right",
    "turn_slight_left":  "slight_left",
    "turn_slight_right": "slight_right",
    "turn_sharp_left":   "sharp_left",
    "turn_sharp_right":  "sharp_right",
    "u_turn":            "u_turn",
    "keep_left":         "keep_left",
    "keep_right":        "keep_right",
    "destination":       "destination",
}

class NavitBridge:
    def __init__(self):
        self.ser = serial.Serial(SERIAL_PORT, BAUD, timeout=1)
        dbus.mainloop.glib.DBusGMainLoop(set_as_default=True)
        bus = dbus.SessionBus()
        obj = bus.get_object("org.navit_project.navit",
                             "/org/navit_project/navit/default_navit")
        iface = dbus.Interface(obj, dbus_interface="org.navit_project.navit")
        cb_path = iface.callback_attr_new()
        for attr in WATCHED:
            iface.add_attr(cb_path, attr)
        bus.add_signal_receiver(
            self.on_update,
            signal_name="callback_attr_update",
            dbus_interface="org.navit_project.navit",
            path=cb_path,
        )

    def on_update(self, attr_name, value):
        msg = None
        if attr_name == "navigation_next_turn":
            code = MANEUVER_MAP.get(str(value), str(value))
            msg = f"NAV:TURN:{code}\n"
        elif attr_name == "navigation_distance_turn":
            msg = f"NAV:DIST:{int(value)}\n"
        elif attr_name == "navigation_street_name":
            msg = f"NAV:STREET:{str(value)[:20]}\n"
        elif attr_name == "navigation_status":
            msg = f"NAV:STATUS:{str(value)}\n"
        elif attr_name == "eta":
            msg = f"NAV:ETA:{int(value)}\n"
        elif attr_name == "destination_length":
            msg = f"NAV:REMAIN:{int(value)}\n"
        elif attr_name == "position_direction":
            msg = f"NAV:HEAD:{int(value)}\n"
        elif attr_name == "position_time_iso8601":
            msg = f"NAV:TIME:{str(value)}\n"
        elif attr_name == "position_coord_geo":
            # value is typically (lng, lat) or struct; adapt to your D-Bus binding
            try:
                lat, lon = float(value[1]), float(value[0])  # (lng, lat) from Navit
                msg = f"NAV:POS:{lat:.4f},{lon:.4f}\n"
            except (IndexError, TypeError, ValueError):
                pass
        if msg:
            self.ser.write(msg.encode())

    def run(self):
        GLib.MainLoop().run()

if __name__ == "__main__":
    NavitBridge().run()

3. Serial Protocol (Host → Pico, 115200 baud, newline-terminated ASCII)

The same protocol is used regardless of whether the transport is USB CDC or Bluetooth SPP.

Feature toggles (clock screen): Send CFG:<name>:0 or CFG:<name>:1 to enable or disable what is shown. Clock/ETA/compass/remain default to 1 (on). CAN bus is supported by the firmware but disabled by default (0).

4. Transport — USB CDC or Bluetooth SPP

The host device can connect to the Pico over either transport. The Pico listens on both
USB CDC and Bluetooth SPP simultaneously.

USB CDC

• Connect a USB cable from the host to the Pico USB port
• Pico appears as /dev/ttyACM0 (Linux) or equivalent on Android
• Also provides 5 V power to the Pico via VSYS — no separate power supply needed
• Baud rate: 115200

Bluetooth SPP

• Pico advertises as FIS-Bridge using classic Bluetooth SPP via BTstack (onboard CYW43439)
• No external Bluetooth module required
• Pair once: scan for FIS-Bridge, enter PIN 0000 if prompted — reconnects automatically
• On Linux: Pico appears as /dev/rfcomm0 after pairing
• Baud rate: 115200

If using Bluetooth only (no USB), the Pico needs a separate 5 V power source via the VSYS
pin — e.g. a car USB adapter or a 12 V → 5 V regulator on the PCB.

5. Hardware

5.1 Controller — Raspberry Pi Pico 2 W

5.2 The 3LB (Three-Line Bus)

Bus runs at 5 V logic, 2300 Hz,Pico GPIO is 3.3 V — level shifting required on all lines.

Bus arbitration: Before transmitting, a master raises ENA to claim the bus. If ENA is already
high it waits. The cluster acknowledges with a 100 µs pulse. The Pico and ECU safely share the
bus without any relay or switch.

5.3 Level Shifting

6× BS170 N-channel MOSFET (TO-92, through-hole), one per 3LB GPIO line (3 RX + 3 TX).
Each channel uses two 2.2 kΩ pull-up resistors — one to 3.3 V, one to 5 V. Use non-inductive resistors (e.g. metal film or SMD thick/thin film); avoid wirewound types.

BS170 pinout (flat face toward you, left to right): Source — Gate — Drain.

5.4 Instrument Cluster Connector (Green T32a)

Connector type: Kostal MLK 1.2 / MQS 0.63 mm. Use a VAG pin tool to back-probe terminals.
Do not cut harness wires unless you are absolutely sure what you are doing.
One can cut the wires needed, add female and male that can connect together or to ECU and gauge cluster side connectors on the PCBs headers. Then it easy to remove the pcb for repairs and restore original function.

5.5 Inline PCB Connector

JST PH 2.00 mm pitch, 3-position, one pair each side. Makes the PCB fully removable —
unplug both sides and connect them directly to bypass the board.

Any 3-position single-row 2.00 mm pitch THT header is a suitable alternative for the PCB header.

5.6 Pico 2 W GPIO Pinout

3LB RX — monitor ECU frames, detect bus idle (inputs, via level shifter):

3LB TX — inject frames during idle gaps (outputs, via level shifter):

Optional CAN (when CAN enabled, MCP2561): The CAN controller used is the MCP2561. It has only 2 signal connections: TXD and RXD. 3.3 V logic; no level shifter needed. See firmware/fis_can.h and firmware README.

MCP2561 CANH/CANL connect to vehicle comfort/infotainment CAN (100 kbit/s). For when to add a 120 ohm termination (tapped in middle vs replacing radio vs bench), see firmware README.

5.7 Cluster Coding Prerequisite

Code the cluster using VCDS or OBDeleven, Module 17 — Instruments:
enable "Navigation present". Without this the navigation slot in the FIS/MFA is inactive
even if the Pico sends correct 3LB frames.

6. The 3LB Protocol

6.1 Open Source Libraries (Reference)

The Pico firmware reimplements 3LB directly in PIO state machines timed to the BAP FCNav
SDP30DF48V280F specification — no Arduino library dependency.

6.2 Display

The FIS/MFA (Fahrerinformationssystem / Multifunktionsanzeige) screen is a 64×88 pixel
monochrome LCD, 1-bit. Navigation maneuver icons are pre-generated 64×64 px 1-bit arrays
stored in flash (firmware/fis_nav_icons.h) and rendered with:

GraphicFromArray(x, y, width, height, array, 0); // 0 = flash/PROGMEM

6.3 OEM radio: CAN time and display (reference only)

The original VW radio set the instrument cluster time via the CAN bus (CAN-H / CAN-L), using time it received from the FM RDS network. This project does not use CAN for the clock; the Pico sets the FIS clock from GPS (Navit) over serial and 3LB only. The following is documented for reference.

OEM messages not implemented: The specific CAN messages below (mDiagnose_1, mEinheiten) are not implemented. The firmware does support optional CAN bus (MCP2561, disabled by default); the FIS clock is driven solely by the serial protocol (NAV:TIME, timezone conversion, and 3LB injection) described earlier.

mDiagnose_1 (0x7D0) — date and time

Sent cyclically every 1000 ms.

mEinheiten (0x60E) — display format

Sent cyclically every 1000 ms.

6.4 Other potentially useful CAN messages (reference only)

The following CAN frames are not yet implemented in the firmware. They are documented for reference. The firmware supports optional CAN bus (MCP2561, disabled by default) for future use (e.g. to read cluster/vehicle state or adapt FIS output).

Useful for FIS/display

• mKombi_1 (0x320) — sent by the cluster, 10 ms cyclic: KO1_kmh (vehicle speed, bytes 4–5, 15 bits), KO1_angez_kmh (displayed speed including offset, bytes 6–7), KO1_Tankinhalt (fuel level), KO1_Warn_Tank (low fuel, 7 L), KO1_Oeldruck (oil pressure warning), KO1_Kuehlmittel (coolant warning), KO1_Vorgluehen (glow plug, diesel).
• mKombi_2 (0x420) — from cluster, 200 ms cyclic: KO2_gef_Auss_T / KO2_Aussen_T (outside temperature), KO2_Bel_Displ (display brightness %, for dimming FIS at night), KO2_Fehlereintr (fault stored).
• mEinheiten (0x60E) — units: EH1_Uhr_Anzeige (12h/24h), EH1_Datum_Anzeige (EU/US date), EH1_Wochentag (day of week 1=Mon…7=Sun), EH1_Einh_Temp (°C/°F), EH1_Einh_Strck (km/miles).

Situational awareness

• mGate_Komf_1 (0x390), 100 ms: GK1_Rueckfahr (reverse), GK1_Warnblk_Status (hazards), GK1_Bremslicht, GK1_Abblendlicht / GK1_Fernlicht (headlights/high beam), GK1_Wischer_vorn (wipers), GK1_SH_laeuft (aux heater), door status (driver, passenger, rear L/R).
• mZAS_1 (0x572) — ignition: ZA1_Klemme_15 (ignition on), ZA1_Klemme_50 (starter), ZA1_S_Kontakt (key in).
• mClima_1 (0x5E0) — CL1_Kompressor (A/C on), CL1_Hecksch / CL1_Frontsch (rear/front screen heat), CL1_Restwaerme (residual heat).

Parking (if equipped)

• Parkhilfe_01 (0x497) — PDC: obstacle front/rear, beeper active, audio ducking request, system state.

Other

• mKombi_3 (0x520) — KO3_Kilometer (odometer), KO3_Standzeit (parked duration).
• mSysteminfo_1 (0x5D0) — SY1_Fzg_Derivat (body style), SY1_Notbrems_Status (emergency braking).

Signal reference tables

mKombi_1 — 0x320 (from cluster, 10 ms cyclic)

KO1_angez_kmh spans bytes 6–7 (10 bits from bit 6); KO1_kmh spans bytes 4–5 (15 bits from bit 1). Little-endian.

mKombi_2 — 0x420 (from cluster, 200 ms cyclic)

Temperature: °C = (raw × 0.5) − 50. Raw 0xFF = invalid.

mEinheiten — 0x60E (1000 ms cyclic)

mGate_Komf_1 — 0x390 (100 ms cyclic)

mZAS_1 — 0x572 (ignition/key)

mClima_1 — 0x5E0

Parkhilfe_01 — 0x497 (if equipped)

mKombi_3 — 0x520

KO3_Standzeit = time since last ignition-off in 4-second steps (max ~36.4 h).

mSysteminfo_1 — 0x5D0

7. Firmware Runtime Behaviour

Core 0:

• Initialises USB CDC and BTstack SPP (FIS-Bridge, PIN 0000)
• Reads NAV:*, BT:*, and CFG:* messages from both interfaces non-blocking
• Updates shared nav_state_t and feature toggles (fis_config_t) under a critical section
• When CAN is enabled (CFG:CAN:1), runs optional CAN poll (firmware supports CAN; stub until MCP2561 driver is completed)

Core 1:

• Monitors 3LB ENA/CLK/DATA via PIO SM0 (RX sniffer)
• Detects idle gaps between ECU transmissions
• When bus is idle, checks nav_state_t and feature toggles (fis_config_t), then injects:
  • Active call → call frame (highest priority)
  • Active navigation (routing / recalculating) → nav icon + street name + distance
  • Media info present, no nav → track name frame
  • Clock enabled and GPS time available → clock frame (local time on line 1; line 2: remain / ETA / compass / date per toggles)
  • Otherwise → do nothing; ECU frames reach FIS/MFA unmodified

Injection: Wait ENA LOW (bus idle) → raise ENA → transmit via PIO SM1 → lower ENA → ECU resumes.

8. Software Stack Summary

9. Key References

Platform: VW Passat B6 (3C), 2005–2010, PQ46 platform.
Cluster part numbers: 3C0 920 8xx series.
FIS/MFA screen: 64×88 px monochrome LCD, 1-bit, 3LB protocol.