Do all microcontrollers come with a serial port?

No, not all microcontrollers come with a serial port. The presence and number of serial ports depend on the microcontroller's architecture, target application, and price point.

Here's a detailed breakdown:

1. Common Serial Communication Interfaces

When we say "serial port," we typically refer to these common interfaces:

• UART/USART (TTL level, e.g., 3.3 V or 5 V): Very common, but not universal. Some tiny 8-bit MCUs (e.g., certain ATtiny, PIC10/12) have no hardware UART.

• RS-232 (±3–±12 V): Almost no MCUs output true RS-232 levels directly—you need a transceiver (e.g., MAX232).

• USB device/host: Only MCUs with an integrated USB controller support this natively; many dev boards fake it using a USB-to-UART bridge (CP2102/CH340/FT232).

• Other serial buses: I²C, SPI, CAN, LIN, 1-Wire—common, but presence depends on the part.

2. Microcontroller Categories & Serial Port Availability

A. Microcontrollers WITH Serial Ports (Most Common)

• Most 8-bit MCUs: Arduino (ATmega), 8051, PIC16/18

• 32-bit ARM Cortex-M: STM32, GD32, NXP LPC, Microchip SAM

• ESP series: ESP32, ESP8266 (multiple UARTs)

• Modern PIC32: PIC32MX, PIC32MZ

Example: The STM32F103 (Blue Pill) has:

• 3 x USART

• 2 x I²C

• 2 x SPI

• 1 x USB

B. Microcontrollers WITHOUT Serial Ports (Less Common)

• Very simple 8-bit MCUs: TinyAVR (ATtiny series), PIC10/12

• Ultra-low-cost Chinese MCUs: Some STC8 series variants

• Minimalist embedded processors: Some Padauk, Holtek, or Elan chips

Example: ATtiny13A - Very limited I/O, no hardware UART

3. Workarounds When Hardware UART is Unavailable

Even if a microcontroller lacks hardware serial support, you can implement it in software:

Bit-Banging (Software UART)

// Simple software UART transmit implementation
void soft_uart_tx(char data) {
    // Start bit
    TX_PIN = 0;
    delay_us(bit_time);
    
    // Data bits (8 bits)
    for(int i = 0; i < 8; i++) {
        TX_PIN = (data >> i) & 1;
        delay_us(bit_time);
    }
    
    // Stop bit
    TX_PIN = 1;
    delay_us(bit_time);
}

Pros and Cons of Software UART:

4. How to Check if a Microcontroller Has Serial Ports

Look in the Datasheet for:

• Peripheral List: Check for UART/USART modules

• Pinout Diagram: Look for TX/RX, MOSI/MISO, SCL/SDA pins

• Register Map: Search for UART-related registers

Common Indicators:

// If you see registers like these, it has hardware UART:
UARTx_DR    // Data register
UARTx_SR    // Status register  
UARTx_BRR   // Baud rate register
UARTx_CR1   // Control register

5. Practical Advice for Selection

When you NEED hardware UART:

• High-speed data transfer (>9600 baud)

• Real-time communication

• Low CPU usage requirements

• Reliable communication in interrupt-heavy applications

When software UART is acceptable:

• Low-speed communication (≤9600 baud)

• Simple sensor reading

• Projects with plenty of CPU cycles

• Cost-sensitive applications

6. Modern Trends

• More serial peripherals: Modern MCUs tend to include multiple UARTs, SPI, I²C

• Specialized interfaces: CAN, LIN, USB, Ethernet on higher-end MCUs

• Configurable peripherals: Some MCUs allow pin remapping for serial interfaces

Summary Answer:

No, not all microcontrollers have hardware serial ports, but the vast majority of modern, general-purpose microcontrollers do. When selecting a microcontroller for a project requiring serial communication, always verify the peripheral list in the datasheet. If hardware UART is unavailable, software implementation (bit-banging) is a viable alternative for low-speed applications.