KAT/docs/scher_khan.md

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Scher-Khan Protocol

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

Overview

Scher-Khan is decode-only. PWM: 750 µs = 0, 1100 µs = 1; preamble uses 2× short then alternating. Variable bit count (35, 51, 57, 63, 64, 81, 82); only 51-bit format is parsed for serial/button/counter. Reference: phreakerclub.com/72.

Timing

Parameter	Value	Notes
Short (0)	750 µs	±160 µs
Long (1)	1100 µs	±160 µs
Min bits	35	(variable)

Encoding

PWM; preamble: two short then alternating short/long.

Frame Layout (variable)

• 51-bit format: serial (28) | button (4) | counter (16) — “MAGIC CODE” / Dynamic; parsed for serial/btn/cnt.
• Other lengths (35, 57, 63, 64, 81, 82) decoded as raw bit count but not field-parsed.

Decoder Steps

1. Reset — Wait for preamble (2 short + alternating).
2. CheckPreamble — Confirm preamble pattern.
3. SaveDuration — Store pulse duration.
4. CheckDuration — Short–short = 0, long–long = 1 (or equivalent); add bit; on end marker, if bit_count in {35,51,57,63,64,81,82} return decode (51-bit parsed for fields).

Encoder

Not implemented (no encoder in reference).

Frequencies

433.92 MHz.