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RS-422

Balanced differential serial signaling for robust point-to-point links.

Status Examples Runtime example Source posture
draft-core-lab synthetic/passive not yet available standards metadata plus tooling context

Identity

Balanced differential serial signaling for robust point-to-point links.

What This Protocol Teaches

  • Balanced signaling changes observation but not semantic authority.
  • Point-to-point differential links can carry many byte protocols.
  • Direction and pair identification are part of field interpretation.

Operational Context

RS-422 / TIA-422 appears in embedded, board-level contexts and is modeled in the atlas at the physical layer(s). The binder treats it as an inspection surface: what evidence appears, what timing matters, and what outside authority is required before assigning meaning.

Draft status

draft-core-lab: this page is in Core Lab scope but is not yet promoted to final copy. It has a source-grounded artifact and review structure; it still needs the same page-specific depth as CAN, DBC, MIL-STD-1553, UART, ARINC 429, and Modbus RTU before final-copy status.

A Concrete Artifact

# synthetic observation
A/B differential pair: burst every 100 ms, decoded bytes 24 47 50 ... under 8N1 hypothesis

Synthetic

Synthetic offline sample for explanation; not a real operational trace or live-system instruction.

Worked Decode

  1. The differential pair provides robust electrical evidence for a serial waveform.
  2. A byte decode still requires baud/framing assumptions.
  3. The bytes may carry NMEA, proprietary serial, or another application protocol.
  4. RS-422 itself does not define message boundaries.

Field Layout / Anatomy

Element Shape Inspection meaning
Balanced pair two wires Receiver sees voltage difference.
Driver/receiver point-to-point Authority usually comes from one talker.
Termination electrical design Affects signal integrity, not semantics.
Byte protocol external Defines message meaning.

Visual Model

flowchart LR tx["Driver"] --> pair["Balanced pair"] pair --> rx["Receiver"] observer["Offline captured evidence"] -. inspected as .-> pair pair --> bytes["Byte-stream hypothesis"]

Timing And Authority

Electrical timing supports the serial stream; semantic authority begins at the byte protocol.

Semantic authority

RS-422 authority ends at the electrical interface. The 24 47 50 ... bytes only gain message meaning from the carried byte protocol and its source documentation; stable differential signaling does not identify that protocol.

Failure And Ambiguity

  • Swapped polarity can invert the stream.
  • Point-to-point assumptions fail if installers build nonstandard multidrop wiring.
  • Byte-level decodes can be stable under wrong higher-layer protocol.

Observer Lesson

A passive observer can infer bursts, baud hypotheses, and direction. It cannot infer message semantics without the carried protocol.

Python Model

No current runtime example is claimed for this draft page. Keep reader claims at the artifact and source level until a separate implementation plan adds a tested model.

Local Teaching Notes

Simplification

The example is synthetic and omits electrical compliance.

Source Confidence

Source confidence is medium for scope and terminology, with semantic claims limited to public metadata, public source notes, and synthetic teaching artifacts.

Source Notes

Field Value
Governance tier Tier 1 Core Lab (planned; no runtime example)
Canonical source status yes
Public explainer status no
Open-source tool status no
Sample-data status none listed; use synthetic teaching artifacts
Confidence medium
Citation specificity document-metadata-level
Canonical source(s) TIA/EIA-422 balanced voltage digital interface circuits (TIA; TIA/EIA-422; paywalled; metadata-only)
Public explainer/tooling source(s) none listed in atlas
Open-source tool references none listed in atlas

References

Public Sources