Serial ports, also known as serial data interfaces, are communication interfaces for transmitting data in a serial manner, where data bits are transferred one after the other over a single channel. This contrasts with parallel data interfaces, where multiple data bits are transmitted simultaneously. Below are some of the most commonly used types of serial interfaces.

  1. I2C

  2. SPI

  3. RS232

  4. RS422

  5. RS485

  6. USB

Related article:

Serial Port Server Selection Guide

Serial Port vs Parallel Port:Difference and Comparison

Classification and Application of Serial Port Baud Rate

 I2C Interface

The I2C interface is primarily used for communication between integrated circuit chips. Originally developed by Philips, it is a simple, two-wire synchronous serial bus.

When using I2C, only two wires are needed for data transmission. The main pins are:

  • SCL: Serial Clock Line

  • SDA: Serial Data Line

I2C supports different transmission speeds depending on the mode, which can be categorized as:

  • Standard Mode: Maximum speed of 100 Kbps (kilobits per second)

  • Fast Mode: Maximum speed of 400 Kbps

  • Fast Mode Plus: Maximum speed of 1 Mbps (megabit per second)

  • High-Speed Mode: Maximum speed of 3.4 Mbps

  • Ultra-Fast Mode: Maximum speed of 5 Mbps (only supports unidirectional transmission and is not compatible with other modes)

     

     

Related article

20230911c_1.jpg

SPI Interface

The SPI (Serial Peripheral Interface) is used for synchronous serial data transmission between low-speed devices such as EEPROM, FLASH, real-time clocks, and ADCs. Initially defined by Motorola for its MC68HCXX series processors, SPI uses four lines for data transmission:

  • MOSI (Master Out, Slave In): Data output from the master device to the slave.

  • MISO (Master In, Slave Out): Data input to the master device from the slave.

  • SCLK (Serial Clock): Clock signal generated by the master device.

  • NSS (Slave Select): Signal to enable the slave device, controlled by the master.

SPI communication operates in two modes:

  1. Low-Speed SPI: Typically used in low-power, long-distance communications with speeds of a few hundred kHz.

  2. High-Speed SPI: Used for high-speed data transfer, with speeds reaching tens of MHz or even higher.

    图片.png

RS232 Interface

RS232 is a communication interface widely used for industrial control and computer peripherals. It was standardized by the Electronic Industries Association (EIA) in 1970. RS232 typically uses DB9 (9 pins) or DB25 (25 pins) connectors.

 

图片.png

 

Main pins include

  • RSD: Receive Signal Detect

  • RXD: Receive Data

  • TXD: Transmit Data

  • DTR: Data Terminal Ready

  • GND: Ground

  • DSR: Data Set Ready

  • RTS: Request to Send

RS232 supports various fixed transmission rates, including 50, 75, 110, 150, 300, 600, 1200, 2400, 4800, 9600, 19200 bps, and can now go up to a maximum of 230400 bps.

RS422 Interface

RS422 is an evolution of RS232, providing a balanced communication method that allows for a higher transmission rate of up to 10 Mbps and a transmission distance of up to 4000 feet (under 100 Kbps). RS422 supports single-ended transmission from one transmitter to multiple receivers and uses differential signals for better noise immunity.

图片.png

The main pins are:

  • T+: Transmit Data Positive

  • T-: Transmit Data Negative

  • R+: Receive Data Positive

  • R-: Receive Data Negative

  • GND: Ground

RS422 is commonly used in industrial control systems.

RS485 Interface

RS485 builds on RS422 by adding multipoint, bidirectional communication capabilities. Like RS422, RS485 uses differential signaling for long-distance and noise-immune data transmission. However, unlike RS422, RS485 requires only two wires for data transmission, and thus supports half-duplex communication, meaning data cannot be sent and received simultaneously.

RS485 is often used in industrial and noisy environments and can utilize twisted pair shielded cables for further signal protection.

图片.png

USB Interface

USB (Universal Serial Bus) is a high-speed serial interface commonly used for communication between computers and devices like storage drives, printers, and scanners. USB transfer speeds vary by version:

图片.png

 

  • USB 1.0:

    • Low-Speed: 1.5 Mbit/s (0.1875 MB/s)

    • Full-Speed: 12 Mbit/s (1.5 MB/s)

  • USB 1.1 (Full-Speed): Maximum speed of 12 Mbit/s (1.5 MB/s)

  • USB 2.0 (Hi-Speed): Maximum speed of 480 Mbit/s (60 MB/s)

  • USB 3.0 (SuperSpeed): Maximum speed of 5 Gbit/s (600 MB/s)

  • USB 3.1:

    • Gen 1 (USB 3.0): Maximum speed of 5 Gbit/s (600 MB/s)

    • Gen 2: Maximum speed of 10 Gbit/s (1250 MB/s)

  • USB 3.2:

    • Gen 1: Maximum speed of 5 Gbit/s (600 MB/s)

    • Gen 2: Maximum speed of 10 Gbit/s (1250 MB/s)

    • Gen 2x2 (Type-C): Maximum speed of 20 Gbit/s (2500 MB/s)

  • USB 4 (Type-C only): Maximum speed of 40 Gbit/s (5000 MB/s)

Introducing the E810-U15H Industrial Serial Converter

The E810-U15H is an industrial-grade serial converter that supports various interfaces including USB, RS485, RS232, RS422, and TTL. Featuring an FTDI imported chip, the converter offers a transmission rate of up to 12 Mbps. It is designed to meet industrial-grade standards, with ESD protection, PTC self-resetting fuses, and dual isolation for power and signal, ensuring stable operation even in harsh environments.