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  "title": "MODBUS combined register operation order",
  "system": "MODBUS Application Protocol V1.1b3",
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  "evidence_state": "PRIMARY_DOCUMENTATION_REVIEW_ONLY",
  "canonical_question": "In MODBUS function 23, is the returned register data captured before the write operation?",
  "near_questions": [
    "Does MODBUS function 0x17 read before writing?",
    "Can overlapping read/write ranges return the newly written value?",
    "Does a function 23 response prove a physical actuator moved?",
    "Does combined register access establish safe retry after timeout?"
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      "claim": "MODBUS function 23 decimal, 0x17, combines a write and a read of holding registers, with the write performed before the read. Returned data must be interpreted in that order, especially when the ranges overlap. This ordering does not establish physical actuator completion, safe repetition after a lost response, or a broader database transaction guarantee.",
      "reliance": "DOCUMENTED_CAPABILITY_ONLY"
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    "Buyer implementation, live runtime enforcement, settled payment, physical outcome, certification or permission to act are not established.",
    "No expanded capabilities or licences for existing INDEX executables."
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  "public_summary": "MODBUS function 23 decimal, 0x17, combines a write and a read of holding registers, with the write performed before the read. Returned data must be interpreted in that order, especially when the ranges overlap. This ordering does not establish physical actuator completion, safe repetition after a lost response, or a broader database transaction guarantee.",
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    "source_title": "MODBUS Application Protocol V1.1b3",
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    "bounded_answer": "MODBUS function 23 decimal, 0x17, combines a write and a read of holding registers, with the write performed before the read. Returned data must be interpreted in that order, especially when the ranges overlap. This ordering does not establish physical actuator completion, safe repetition after a lost response, or a broader database transaction guarantee.",
    "required_buyer_context": "Function code and register ranges; Written values and returned data; Device semantics and independent physical outcome. Buyer deployment not inspected.",
    "missing_evidence": "A broader claim needs evidence matching the intended use. Payment does not upgrade the evidence state."
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  "private_boundary": "Raw logs, thresholds, private paths, source code, protected mechanisms and reconstruction-level details are excluded from public and paid delivery.",
  "decision_profile": {
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    "documented_statement": {
      "status": "documented",
      "statement": "MODBUS function 23 decimal, 0x17, combines a write and a read of holding registers, with the write performed before the read. Returned data must be interpreted in that order, especially when the ranges overlap. This ordering does not establish physical actuator completion, safe repetition after a lost response, or a broader database transaction guarantee.",
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    },
    "review_inference": {
      "status": "review_inference",
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    "buyer_evidence_required": [
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      "Written values and returned data",
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    "review_condition": {
      "status": "varexis_review_policy",
      "statement": "Refuse buyer-specific assurance from documentation alone. Ordering alone is not an atomicity, concurrency isolation, physical actuator completion, or non-idempotent retry guarantee. It does not close ICE02-F036."
    },
    "unknowns": "The buyer implementation, effective configuration, complete evidence inventory and actual business outcome were not inspected.",
    "unknown_finding": {
      "status": "unknown",
      "statement": "The buyer implementation, effective configuration, complete evidence inventory and actual business outcome were not inspected."
    },
    "evidence_sources": [
      {
        "source_id": "modbus-1-1b3",
        "url": "https://www.modbus.org/file/secure/modbusprotocolspecification.pdf",
        "final_url": "https://www.modbus.org/file/secure/modbusprotocolspecification.pdf",
        "status": 200,
        "captured_at_utc": "2026-10-25T20:04:29.497Z",
        "sha256": "f80d0d7132fd035104c3f21b01026470e3310ca3d8d493d9a9737d0d32ad2eb1",
        "bytes": 932519,
        "title": "MODBUS Application Protocol V1.1b3",
        "hash_basis": "SHA-256 of unmodified HTTP response body bytes",
        "rights_review": "Original factual paraphrase and citation only. Modbus Organization retains rights in its specification. The captured PDF, figures and tables remain private; no standard or implementation code is redistributed.",
        "checked_on": "2026-10-25",
        "capture_status": 200,
        "claim_review_completed": true,
        "reviewed_sections": [
          "Section 7, exception code 05",
          "Section 7, exception code 06",
          "Section 7, exception code 03",
          "Section 6.21",
          "Section 6.17"
        ],
        "version_context": "MODBUS Application Protocol V1.1b3, dated April 26 2012; device function support and physical behavior unverified."
      }
    ],
    "observed_deployment": false,
    "commercial_reliance_boundary": "Documentation review only; the buyer must establish applicability and actual outcomes. INDEX does not inspect or control the deployment.",
    "paid_value": {
      "decision_context": "Interpret combined read/write evidence with the documented write-before-read ordering.",
      "free": "Complete review, practical questions, sources and limitations; may be saved locally.",
      "single_request": "Existing server-saved version-bound route snapshot for later authenticated retrieval.",
      "evidence_receipt": "The same snapshot plus the existing unsigned delivery receipt.",
      "excluded": [
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        "Continuous monitoring or change alerts",
        "Testing the buyer configuration",
        "Private evidence or vendor certification"
      ],
      "integrity": "Hashes identify content versions; they do not prove truth or provide a signature."
    },
    "revalidation": {
      "trigger": "A saved purchase does not recheck the source or buyer configuration.",
      "specific_watch": "Recheck Section 6.17 in MODBUS Application Protocol V1.1b3 when the source, applicable version, configuration or intended reliance changes. A detected change creates a review candidate, not automatic approval."
    },
    "buyer_relevance": "Interpret combined read/write evidence with the documented write-before-read ordering.",
    "refusal_conditions": [
      "Refuse buyer-specific assurance from documentation alone. Ordering alone is not an atomicity, concurrency isolation, physical actuator completion, or non-idempotent retry guarantee. It does not close ICE02-F036."
    ]
  },
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    "niche_id": "agent-authority-action-evidence",
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    "buyer_intent": "Interpret combined read/write evidence with the documented write-before-read ordering.",
    "comparison_role": "supplementary_discovery"
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  "paid_access_note": "The full published answer and boundaries are free. Paid access saves the selected route and source versions, with an unsigned receipt when purchased. Preview coverage before paying. Fresh research, bespoke assessment and protected evidence are excluded.",
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  "authority_boundary": "VAREXIS-INDEX informs evidence reliance. It does not provide advice, certification, deployment authority, security assurance, production approval, or guarantee.",
  "human_page": "/varexis-index/catalog.html#modbus-read-write-sequence",
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