ISO 11783-14 — sequence control

Part 14 automates sequences of actions. Its most familiar face is headland management: at the end of a pass, the machine raises the hitch, folds a marker, disengages sections, and lifts the implement — in a defined order, from one operator action or a position trigger. Sequence Control is the protocol that coordinates that.

Why this exists

Turning at the headland is a choreography of half a dozen actuator actions that must happen in the right order every time. Doing it by hand, every pass, is tiring and error-prone. Sequence Control lets the machine record the choreography once and replay it reliably, with each participating ECU executing the steps it owns.

Master and client

   MASTER (runs the saved sequence)            CLIENTS (execute their steps)
     │ ── start sequence ──────────────────►  (all)
     │ ── step 3: "raise rear hitch" ──────►  hitch ECU executes
     │ ◄── step 3 complete ─────────────────  hitch ECU reports
     │ ── step 4: "disengage section bank" ►  section ECU executes
     │ ◄── step 4 complete ─────────────────
     │     … pause / resume / abort as needed …
     │ ── sequence complete ───────────────►

The master drives ordering and timeouts; each client executes the steps addressed to it and reports progress. The protocol carries pause, resume, and abort so a sequence can be interrupted safely.

How machbus expresses it

machbus implements both roles: ScMaster runs and broadcasts the sequence; ScClient executes steps and reports completion. Both surface their lifecycle as ScEvent variants (state changes, step started/completed, sequence complete, timeout, pause/resume/abort).

   ctrl.with_mut::<ScMaster, _>(|m| { m.add_step(step)?; m.start() })?;
   // progress arrives as Event::Sc(ScEvent::MasterStepCompleted { step_id }) …

From concept to code

Failure modes worth knowing

• Step never completes — a client that cannot perform a step must report, or the master times out; do not hang the sequence.
• Unsafe abort — aborting mid-sequence must leave the machine in a safe state, not half-folded.
• Ordering assumptions — steps run in the master’s order; clients should not reorder.

See also

• TIM (AEF) — the authority model often paired with automated motion.
• Implement control, the tractor ECU, and the rest.