| Name | Layer Type | Physical Medium / Interface | Protocol | Addressing | Speed | Topology | Use Case / Example |
|---|---|---|---|---|---|---|---|
| UART | Hardware module | TTL (3.3V/5V, point-to-point) | None (raw byte stream) | No | ~115.2 kbps - 1 Mbps | Point-to-point | MCU to GPS, Debugging |
| RS232 | Physical layer | Serial cable (±12V signals) | Often carries UART or Modbus RTU | No | ~115.2 kbps | Point-to-point | Legacy PCs, industrial machines |
| RS485 | Physical layer | Twisted pair (differential) | Often carries Modbus RTU | Yes (multi-device) | Up to 10 Mbps (typ. <1 Mbps) | Multi-drop bus (1 master, many slaves) | Long-distance industrial sensors |
| I²C | Protocol + physical | SDA/SCL, open-drain (short range) | I²C | Yes | 100 kHz – 3.4 MHz | Multi-master/slave | On-board sensors (EEPROMs, temp) |
| SPI | Protocol + physical | 4 wires (MOSI, MISO, CLK, SS) | SPI | No (each slave has its own SS) | Very high (up to 50 Mbps+) | Point-to-multi-point | Fast peripheral communication |
| Modbus RTU | Protocol | RS232 or RS485 | Modbus | Yes | 9600 – 115.2 kbps | Master/slave | SCADA, industrial devices |
| Modbus TCP | Protocol | Ethernet (RJ45) | Modbus | Yes (IP + unit ID) | 10/100 Mbps | Star (LAN network) | PLCs, remote sensors |
| TCP/IP | Protocol Stack | Ethernet, Wi-Fi, Cellular | Many (HTTP, MQTT, Modbus TCP) | Yes (IP address) | Up to 1 Gbps+ | Star/cloud networks | Web servers, IoT systems |
| Ethernet | Physical + Link Layer | Twisted pair, fiber optics | Carries TCP/IP, UDP, etc. | Yes (MAC/IP) | 10 Mbps – 1 Gbps+ | Star or switch-based | Internet, LANs, remote device mgmt |
| Layer | Example | What It Does |
|---|---|---|
| Application Layer | Modbus, HTTP, MQTT | Structures data, defines "what" to say |
| Transport Layer | TCP, UDP | Ensures reliable delivery (TCP) or fast streaming (UDP) |
| Network Layer | IP (Internet Protocol) | Addresses devices (like 192.168.1.10) |
| Data Link Layer | Ethernet, Wi-Fi | Moves packets between devices on the same network |
| Physical Layer | RS232, RS485, Ethernet cables | Electrical signals, voltages, wires |
| System | How It Connects | Description |
|---|---|---|
| Small sensor board | I²C | Sensor to microcontroller |
| Microcontroller → RS485 | Modbus RTU | Sends data to local PLC over RS485 |
| PLC → SCADA system | Modbus TCP | Over Ethernet with TCP/IP |
| SCADA Dashboard | Web browser | Uses TCP/IP & HTTP or MQTT |
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Serial Communication Protocols - UART, SPI, I2C, RS232, RS485
Watch here -
Modbus Protocol Explained
Watch here -
OSI Model & TCP/IP Stack Explained
Watch here
Think of it like this:
- Physical layer = the wires and voltage (RS232, RS485, Ethernet).
- Communication protocol = the language and rules spoken over those wires (UART, I²C, Modbus, TCP/IP).
- Stacking them together gives you complete communication — from sensor to cloud.