How does Microprocessor command external devices?

A microprocessor commands external devices (like LEDs, motors, displays, sensors, or other peripherals) using three main types of communication buses:

🔌 1. Address Bus

• Purpose: Selects the specific device or memory location.

• The microprocessor sends a unique address to specify which device or I/O port it wants to communicate with.

🔁 2. Data Bus

• Purpose: Transfers data to/from the external device.

• The microprocessor can either send commands/data to a device or receive data from it.

🕹️ 3. Control Bus

• Purpose: Sends control signals to coordinate the operation, like read/write actions.

• Common control signals:

  • RD̅ (Read) – to read from device

  • WR̅ (Write) – to write to device

  • IO/M̅ – to differentiate between I/O and memory access

  • INT – for interrupt handling

🛠️ How It All Works: Step-by-Step

👉 Example: Sending a Command to Turn ON an LED

Assume the LED is connected to an I/O port at address 0x01.

1. Place the address 0x01 on the address bus.

2. Place the data (e.g., 0x01 to turn on LED) on the data bus.

3. Activate the WR̅ (write) signal on the control bus.

4. The external device (LED controller) receives the data and turns on the LED.

🧠 Modes of Communication

🧩 Example Application: Controlling a DC Motor

• The motor driver is connected to a port.

• Microprocessor writes control values to that port (e.g., direction and speed).

• The driver receives the command and powers the motor accordingly.

📦 Real-World Applications

• Home automation: Sending commands to relays, sensors, or displays.

• Robotics: Controlling motors and servos based on sensor data.

• Industrial control: Turning on pumps, alarms, or actuators.

✅ Summary

A microprocessor commands external devices by:

• Addressing them (via Address Bus),

• Transferring data (via Data Bus),

• Controlling operation timing and type (via Control Bus).