Fiat V1 Protocol (Magneti Marelli BSI / PCF7946)

Rust module: src/protocols/fiat_v1.rs Reference: REFERENCES/ProtoPirate/protocols/fiat_v1.c

Overview

Fiat V1 is the Magneti Marelli BSI keyfob protocol (PCF7946), found on Fiat Panda, Grande Punto, and possibly other Fiat/Lancia/Alfa ~2003-2012. Uses Manchester encoding with auto-detected timing from preamble pulse averaging. Two timing variants: Type A (~260 us, e.g. Panda) and Type B (~100 us, e.g. Grande Punto). This is a different protocol from Fiat V0.

Timing

Parameter	Default	Notes
Short	260 us	Auto-detected from preamble
Long	520 us	2x detected TE
Delta	80 us	Minimum 30 us
Preamble	80+ pulses	50-350 us range
Min bits	80	Max 104 bits

Auto-Detection

Preamble pulses (50-350 us) are accumulated. After 80+ pulses, te_detected = te_sum / te_count becomes the reference TE. Type A/B boundary is at 180 us.

Frame Layout (80-104 bits = 10-13 bytes)

Bytes	Content
0-1	Preamble residue (0xFFFF/0xFFFC)
2-5	Serial (32 bits)
6	Button:4 | Epoch:4
7	Counter:5 | Scramble:2 | Fixed:1
8-12	Encrypted payload (40 bits)

Decoder Steps

1. Reset – Wait for HIGH pulse in 50-350 us range. Also detect retransmission gaps (>5000 us).
2. Preamble – Count pulses, accumulate for TE averaging. On gap >= te_detected * 4, transition to Sync.
3. Sync – Expect HIGH sync pulse of te_detected * 4 to te_detected * 12 duration.
4. Data – Manchester decode up to 104 bits into 13-byte raw buffer.
5. RetxSync – After gap >5000 us, look for sync pulse 400-2800 us (retransmission).

Buttons

Code	Name
0x7	Lock
0xB	Unlock
0xD	Trunk

Encoder

Not supported (decode-only).

Frequencies

433.92 MHz.