diff --git a/Cargo.lock b/Cargo.lock
index bb679f8..1aa919b 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -2870,7 +2870,6 @@ dependencies = [
  "futures-core",
  "futures-util",
  "log",
- "smallvec",
  "thiserror",
  "tokio",
  "tokio-util",
diff --git a/Cargo.toml b/Cargo.toml
index 4ecc462..871d2f9 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -27,7 +27,7 @@ serde_json = "1.0.148"
 sqlx = { version = "0.8.6", features = ["runtime-tokio", "sqlite", "derive", "migrate"] }
 thiserror = "2.0.17"
 tokio = { version = "1.48.0", features = ["macros", "rt-multi-thread"] }
-tokio-modbus = "0.17.0"
+tokio-modbus = { version = "0.17.0", default-features = false, features = ["tcp"] }
 tracing = "0.1.44"
 tracing-subscriber = { version = "0.3.22", features = ["fmt", "std", "env-filter", "registry", "json", "tracing-log"] }
 
diff --git a/specs/001-modbus-relay-control/plan.md b/specs/001-modbus-relay-control/plan.md
index 164065c..dbe6f93 100644
--- a/specs/001-modbus-relay-control/plan.md
+++ b/specs/001-modbus-relay-control/plan.md
@@ -8,7 +8,7 @@
 
 **Technical Approach**:
 - **Architecture**: Pragmatic Balance (Service Layer Pattern) - Hexagonal architecture with domain/application/infrastructure/presentation layers
-- **Backend**: Rust with tokio-modbus 0.17.0 for Modbus RTU over TCP, Poem 3.1 for HTTP API with OpenAPI
+- **Backend**: Rust with tokio-modbus 0.17.0 for Modbus TCP, Poem 3.1 for HTTP API with OpenAPI
 - **Frontend**: Vue 3 + TypeScript with HTTP polling (2-second intervals), deployed to Cloudflare Pages
 - **Reverse Proxy**: Traefik on Raspberry Pi with Authelia middleware for authentication and HTTPS termination
 - **Persistence**: SQLite for relay labels
@@ -19,7 +19,7 @@
 
 **Language/Version**: Rust 1.75+
 **Primary Dependencies**:
-- tokio-modbus 0.17.0 (Modbus RTU over TCP)
+- tokio-modbus 0.17.0 with TCP feature only (Modbus TCP protocol)
 - Poem 3.1 + poem-openapi 5.1 (HTTP API with OpenAPI)
 - Tokio 1.48 (async runtime)
 - sqlx 0.8 (SQLite persistence with compile-time verification)
@@ -184,7 +184,7 @@ sta/  (repository root)
 **Action**: Add the following dependencies:
 ```toml
 [dependencies]
-tokio-modbus = { version = "0.17.0", features = ["rtu", "tcp"] }
+tokio-modbus = { version = "0.17.0", default-features = false, features = ["tcp"] }
 sqlx = { version = "0.8", features = ["runtime-tokio", "sqlite"] }
 mockall = "0.13"
 async-trait = "0.1"
@@ -904,7 +904,7 @@ impl RelayLabelRepository for SqliteRelayLabelRepository {
 
 ### Phase 4: Infrastructure - Real Modbus Client (1.5 days)
 
-**Objective**: Implement real Modbus RTU over TCP communication using tokio-modbus.
+**Objective**: Implement real Modbus TCP communication using tokio-modbus.
 
 **Prerequisites**: Phase 1 complete (controller trait), hardware available for testing
 
@@ -2014,7 +2014,7 @@ tests/
 ```toml
 [dependencies]
 # Existing dependencies...
-tokio-modbus = { version = "0.17.0", features = ["rtu", "tcp"] }
+tokio-modbus = { version = "0.17.0", default-features = false, features = ["tcp"] }
 sqlx = { version = "0.8", features = ["runtime-tokio", "sqlite"] }
 mockall = "0.13"
 async-trait = "0.1"
diff --git a/specs/001-modbus-relay-control/research.md b/specs/001-modbus-relay-control/research.md
index 7973e97..47ade9b 100644
--- a/specs/001-modbus-relay-control/research.md
+++ b/specs/001-modbus-relay-control/research.md
@@ -67,10 +67,11 @@
 
 **Version**: tokio-modbus 0.17.0 (latest stable, released 2025-10-22)
 
-**Protocol**: Modbus RTU over TCP (NOT Modbus TCP)
-- Hardware uses RTU protocol tunneled over TCP
-- Includes CRC16 validation
-- Different from native Modbus TCP (no CRC, different framing)
+**Protocol**: Modbus TCP (native TCP protocol)
+- Hardware configured to use native Modbus TCP protocol
+- Uses MBAP (Modbus Application Protocol) header
+- No CRC16 validation (TCP/IP handles error detection)
+- Standard Modbus TCP protocol on port 502
 
 **Connection Strategy**:
 - Shared `Arc<Mutex<Context>>` for simplicity
@@ -92,11 +93,13 @@
 
 ### Critical Gotchas
 
-1. **Device Gateway Configuration**: Hardware MUST be set to "Multi-host non-storage type" - default storage type sends spurious queries causing failures
+1. **Device Protocol Configuration**: Hardware MUST be configured to use Modbus TCP protocol (not RTU over TCP) via VirCom software
+   - Set "Transfer Protocol" to "Modbus TCP protocol" in Advanced Settings
+   - Device automatically switches to port 502 when TCP protocol is selected
 
-2. **No Built-in Timeouts**: tokio-modbus has NO automatic timeouts - must wrap every operation with `tokio::time::timeout`
+2. **Device Gateway Configuration**: Hardware MUST be set to "Multi-host non-storage type" - default storage type sends spurious queries causing failures
 
-3. **RTU vs TCP Confusion**: Device uses Modbus RTU protocol over TCP (with CRC), not native Modbus TCP protocol
+3. **No Built-in Timeouts**: tokio-modbus has NO automatic timeouts - must wrap every operation with `tokio::time::timeout`
 
 4. **Address Indexing**: Relays labeled 1-8, but Modbus addresses are 0-7 (use newtype pattern with conversion methods)
 
@@ -111,8 +114,8 @@
 use tokio_modbus::prelude::*;
 use tokio::time::{timeout, Duration};
 
-// Connect to device
-let socket_addr = "192.168.1.200:8234".parse()?;
+// Connect to device using Modbus TCP on standard port 502
+let socket_addr = "192.168.1.200:502".parse()?;
 let mut ctx = tcp::connect(socket_addr).await?;
 
 // Set slave ID (unit identifier)
@@ -125,6 +128,8 @@ let states = timeout(
 ).await???; // Triple-? handles timeout + transport + exception errors
 ```
 
+**Note**: Modbus TCP uses the standard MBAP header and does not require CRC16 validation. The protocol is cleaner and more standardized than RTU over TCP.
+
 **Toggle Relay with Retry**:
 ```rust
 async fn toggle_relay(
diff --git a/specs/001-modbus-relay-control/tasks.md b/specs/001-modbus-relay-control/tasks.md
index f946ba7..346076b 100644
--- a/specs/001-modbus-relay-control/tasks.md
+++ b/specs/001-modbus-relay-control/tasks.md
@@ -13,25 +13,25 @@
 **Purpose**: Initialize project dependencies and directory structure
 
 - [x] **T001** [Setup] [TDD] Add Rust dependencies to Cargo.toml
-  - Add: tokio-modbus = "0.17.0", sqlx = { version = "0.8", features = ["runtime-tokio", "sqlite"] }, mockall = "0.13", async-trait = "0.1"
+  - Add: tokio-modbus = { version = "0.17.0", default-features = false, features = ["tcp"] }, sqlx = { version = "0.8", features = ["runtime-tokio", "sqlite"] }, mockall = "0.13", async-trait = "0.1"
   - **Test**: cargo check passes
   - **Complexity**: Low | **Uncertainty**: Low
 
-- [ ] **T002** [P] [Setup] [TDD] Create module structure in src/
+- [x] **T002** [P] [Setup] [TDD] Create module structure in src/
   - Create: src/domain/, src/application/, src/infrastructure/, src/presentation/
   - **Test**: Module declarations compile without errors
   - **Complexity**: Low | **Uncertainty**: Low
 
 - [ ] **T003** [P] [Setup] [TDD] Update settings.rs with Modbus configuration
-  - Add ModbusSettings struct with host, port, slave_id, timeout_secs fields
-  - Add RelaySettings struct with label_max_length field
+  - Add ModbusSettings struct with `host`, `port`, `slave_id`, `timeout_secs` fields
+  - Add RelaySettings struct with `label_max_length` field
   - Update Settings struct to include modbus and relay fields
   - **Test**: Settings loads from settings/base.yaml with test Modbus config
   - **Complexity**: Low | **Uncertainty**: Low
 
 - [ ] **T004** [P] [Setup] [TDD] Create settings/base.yaml with Modbus defaults
-  - Add modbus section: host: "192.168.1.100", port: 502, slave_id: 1, timeout_secs: 3
-  - Add relay section: label_max_length: 50
+  - Add modbus section: host: "192.168.0.200", port: 502, slave_id: 0, timeout_secs: 5
+  - Add relay section: label_max_length: 8
   - **Test**: Settings::new() loads config without errors
   - **Complexity**: Low | **Uncertainty**: Low
 
@@ -184,9 +184,9 @@
 
 - [ ] **T024** [US1] [TDD] Write tests for ModbusRelayController
   - **REQUIRES HARDWARE/MOCK**: Integration test with tokio_modbus::test utilities
-  - Test: Connection succeeds with valid config
+  - Test: Connection succeeds with valid config (Modbus TCP on port 502)
   - Test: read_state() returns correct coil value
-  - Test: write_state() sends correct Modbus command
+  - Test: write_state() sends correct Modbus TCP command (no CRC needed)
   - **File**: src/infrastructure/modbus/modbus_controller.rs
   - **Complexity**: High → DECOMPOSED below
   - **Uncertainty**: High
@@ -198,6 +198,7 @@
 **Complexity**: High → Broken into 6 sub-tasks
 **Uncertainty**: High
 **Rationale**: Nested Result handling, Arc<Mutex> synchronization, timeout wrapping
+**Protocol**: Native Modbus TCP (MBAP header, no CRC16 validation)
 
 - [ ] **T025a** [US1] [TDD] Implement ModbusRelayController connection setup
   - Struct: ModbusRelayController { ctx: Arc<Mutex<Context>>, timeout_duration: Duration }
@@ -219,6 +220,7 @@
       {
           use tokio_modbus::prelude::*;
 
+          // Connect using native Modbus TCP protocol (port 502)
           let socket_addr = format!("{}:{}", host, port)
               .parse()
               .map_err(|e| ControllerError::ConnectionError(format!("Invalid address: {}", e)))?;
@@ -244,6 +246,7 @@
   - Private method: read_coils_with_timeout(addr: u16, count: u16) → Result<Vec<bool>, ControllerError>
   - Wrap ctx.read_coils() with tokio::time::timeout()
   - Handle nested Result: timeout → io::Error → Modbus Exception
+  - **Note**: Modbus TCP uses MBAP header (no CRC validation needed)
   - **File**: src/infrastructure/modbus/modbus_controller.rs
   - **Complexity**: Medium | **Uncertainty**: Medium