USB adapter

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FTDI US232R : USB to RS-232 cable FTDI USB SERIAL.jpg
FTDI US232R : USB to RS-232 cable
FTDI TTL-232RG : USB to UART cable FTDI Cable.jpg
FTDI TTL-232RG : USB to UART cable
AdaFruit's FTDI Friend FTDIFriend.jpg
AdaFruit's FTDI Friend

A USB adapter is a type of protocol converter that is used for converting USB data signals to and from other communications standards. Commonly, USB adapters are used to convert USB data to standard serial port data and vice versa. Most commonly the USB data signals are converted to either RS232, RS485, RS422, or TTL-level UART serial data. The older serial RS423 protocol is rarely used any more, so USB to RS423 adapters are less common.

Contents

Uses

USB to serial RS232 adapters are often used with consumer, commercial and industrial applications and USB to serial RS485/RS422 adapters are usually mainly used only with industrial applications. Currently, USB to TTL-level UART converters are used extensively by students and hobbyist as they can be directly interfaced to microcontrollers.

Adapters for converting USB to other standard or proprietary protocols also exist; however, these are usually not referred to as a serial adapter.

The primary application scenario is to enable USB-based computers to access and communicate with serial devices featuring D-Sub (usually DB9 or DB25) connectors or screw terminals, where security of the data transmission is not generally an issue.

USB serial adapters can be isolated or non-isolated. The isolated version has opto-couplers and/or surge suppressors to prevent static electricity or other high-voltage surges to enter the data lines thereby preventing data loss and damage to the adapter and connected serial device. The non-isolated version has no protection against static electricity or voltage surges, which is why this version is usually recommended for only non-critical applications and at short communication ranges.

History

Historically, most personal computers had a built-in D-sub serial RS232 port, also referred to as a COM port, which could be used for connecting the computer to most types of serial RS232 devices. By the late '90s, many computer manufacturers started to phase out the serial COM port in favor of the USB port. By the mid-2000s, some computers had both a serial COM port and a USB port; however, many no longer had a serial COM port by that time, and today most modern computers have no serial COM port but instead only USB ports.

Since many serial devices with a RS232, RS485 or RS422 port are still in use and even still produced today, the disappearance of the serial COM port from personal computers has created a need for the USB to serial adapter.

Architecture

Die of a PL2303HX USB to Serial Bridge Controller manufactured by Prolific Technology. PL2303HX-HD.jpg
Die of a PL2303HX USB to Serial Bridge Controller manufactured by Prolific Technology.

As a simplified example a typical standard USB to serial adapter consists of a USB processor chip which processes the USB signals. The USB processor sends the processed USB signals to a serial driver chip which applies the correct voltages and sends the processed data signals to the serial output. [1]

For the computer to be able to detect and process the data signals drivers must be installed on the computer. Some chip models have drivers installed by default, including FTDI, while drivers for other chip models must be manually installed (e.g. for Windows and MacOS, WCH CH340, [2] Silicon Labs 210x, [3] Prolific PL2303 [4] ).

When the USB to serial adapter is connected to the computer via the USB port the driver on the computer creates a virtual COM port which shows up in Device Manager on Windows, and under /dev on Linux and MacOS. This virtual COM port can be accessed and used as if it was a built-in serial COM port. However, the characteristics of the virtual COM port are not exactly the same as a real internal COM port, mainly due to data latency; which means that if very sensitive and precise data transfer is required, the USB to serial adapter might be unreliable and not a desired solution. [5] Virtual COM drivers are usually available for Windows, Linux and Mac only. [6]

Related Research Articles

In computing, a device driver is a computer program that operates or controls a particular type of device that is attached to a computer or automaton. A driver provides a software interface to hardware devices, enabling operating systems and other computer programs to access hardware functions without needing to know precise details about the hardware being used.

In telecommunications, RS-232, Recommended Standard 232 is a standard originally introduced in 1960 for serial communication transmission of data. It formally defines signals connecting between a DTE such as a computer terminal, and a DCE, such as a modem. The standard defines the electrical characteristics and timing of signals, the meaning of signals, and the physical size and pinout of connectors. The current version of the standard is TIA-232-F Interface Between Data Terminal Equipment and Data Circuit-Terminating Equipment Employing Serial Binary Data Interchange, issued in 1997. The RS-232 standard had been commonly used in computer serial ports and is still widely used in industrial communication devices.

Universal asynchronous receiver-transmitter Computer hardware device

A universal asynchronous receiver-transmitter is a computer hardware device for asynchronous serial communication in which the data format and transmission speeds are configurable. It sends data bits one by one, from the least significant to the most significant, framed by start and stop bits so that precise timing is handled by the communication channel. The electric signaling levels are handled by a driver circuit external to the UART. Two common signal levels are RS-232, a 12-volt system, and RS-485, a 5-volt system.

Serial port Communication interface transmitting information sequentially

In computing, a serial port is a serial communication interface through which information transfers in or out sequentially one bit at a time. This is in contrast to a parallel port, which communicates multiple bits simultaneously in parallel. Throughout most of the history of personal computers, data has been transferred through serial ports to devices such as modems, terminals, various peripherals, and directly between computers.

COM (hardware interface)

COM is the original, yet still common, name of the serial port interface on PC-compatible computers. It can refer not only to physical ports, but also to emulated ports, such as ports created by Bluetooth or USB adapters.

AVR microcontrollers

AVR is a family of microcontrollers developed since 1996 by Atmel, acquired by Microchip Technology in 2016. These are modified Harvard architecture 8-bit RISC single-chip microcontrollers. AVR was one of the first microcontroller families to use on-chip flash memory for program storage, as opposed to one-time programmable ROM, EPROM, or EEPROM used by other microcontrollers at the time.

Serial communication Type of data transfer

In telecommunication and data transmission, serial communication is the process of sending data one bit at a time, sequentially, over a communication channel or computer bus. This is in contrast to parallel communication, where several bits are sent as a whole, on a link with several parallel channels.

GeoPort is a serial data system used on some models of the Apple Macintosh that could be externally clocked to run at a 2 Mbit/s data rate. GeoPort slightly modified the existing Mac serial port pins to allow the computer's internal DSP hardware or software to send data that, when passed to a digital-to-analog converter, emulated various devices such as modems and fax machines. GeoPort could be found on late-model 68K-based machines as well as many pre-USB Power Macintosh models and PiPPiN. Some later Macintosh models also included an internal GeoPort via an internal connector on the Communications Slot. Apple GeoPort technology is now obsolete, and modem support is typically offered through USB.

RS-422

RS-422, also known as TIA/EIA-422, is a technical standard originated by the Electronic Industries Alliance that specifies electrical characteristics of a digital signaling circuit. It was intended to replace the older RS-232C standard with a standard that offered much higher speed, better immunity from noise, and longer cable lengths. RS-422 systems can transmit data at rates as high as 10 Mbit/s, or may be sent on cables as long as 1,200 meters (3,900 ft) at lower rates. It is closely related to RS-423, which used the same signaling systems but on a different wiring arrangement.

1-Wire Device communications bus system

1-Wire is a device communications bus system designed by Dallas Semiconductor Corp. that provides low-speed data, signaling, and power over a single conductor.

RS-485, also known as TIA-485(-A) or EIA-485, is a standard defining the electrical characteristics of drivers and receivers for use in serial communications systems. Electrical signaling is balanced, and multipoint systems are supported. The standard is jointly published by the Telecommunications Industry Association and Electronic Industries Alliance (TIA/EIA). Digital communications networks implementing the standard can be used effectively over long distances and in electrically noisy environments. Multiple receivers may be connected to such a network in a linear, multidrop bus. These characteristics make RS-485 useful in industrial control systems and similar applications.

USB communications device class is a composite Universal Serial Bus device class.

In computer engineering and electrical engineering, bit banging is slang for any method of data transmission that employs software as a substitute for dedicated hardware to generate transmitted signals or process received signals. Software directly sets and samples the states of GPIOs, and is responsible for meeting all timing requirements and protocol sequencing of the signals. In contrast to bit banging, dedicated hardware satisfies these requirements and, if necessary, provides a data buffer to relax software timing requirements. Bit banging can be implemented at very low cost, and is commonly used in embedded systems.

PS/2 port

The PS/2 port is a 6-pin mini-DIN connector used for connecting keyboards and mice to a PC compatible computer system. Its name comes from the IBM Personal System/2 series of personal computers, with which it was introduced in 1987. The PS/2 mouse connector generally replaced the older DE-9 RS-232 "serial mouse" connector, while the PS/2 keyboard connector replaced the larger 5-pin/180° DIN connector used in the IBM PC/AT design. The PS/2 keyboard port is electrically and logically identical to the IBM AT keyboard port, differing only in the type of electrical connector used. The PS/2 platform introduced a second port with the same design as the keyboard port for use to connect a mouse; thus the PS/2-style keyboard and mouse interfaces are electrically similar and employ the same communication protocol. However, unlike the otherwise similar Apple Desktop Bus connector used by Apple, a given system's keyboard and mouse port may not be interchangeable since the two devices use different sets of commands and the device drivers generally are hard-coded to communicate with each device at the address of the port that is conventionally assigned to that device.

UEXT

Universal EXTension (UEXT) is a connector layout which includes power and three serial buses: Asynchronous, I2C, and SPI. The connector layout was specified by Olimex Ltd and declared an open-project that is royalty-free.

MAX232 1987 integrated circuit

The MAX232 is an integrated circuit first created in 1987 by Maxim Integrated Products that converts signals from a TIA-232 (RS-232) serial port to signals suitable for use in TTL-compatible digital logic circuits. The MAX232 is a dual transmitter / dual receiver that typically is used to convert the RX, TX, CTS, RTS signals.

Future Technology Devices International Limited, commonly known by its acronym FTDI, is a Scottish privately held semiconductor device company, specialising in Universal Serial Bus (USB) technology.

Data Terminal Ready (DTR) is a control signal in RS-232 serial communications, transmitted from data terminal equipment (DTE), such as a computer, to data communications equipment (DCE), for example a modem, to indicate that the terminal is ready for communications and the modem may initiate a communications channel.

Arduino Uno

The Arduino Uno is an open-source microcontroller board based on the Microchip ATmega328P microcontroller and developed by Arduino.cc. The board is equipped with sets of digital and analog input/output (I/O) pins that may be interfaced to various expansion boards (shields) and other circuits. The board has 14 digital I/O pins, 6 analog I/O pins, and is programmable with the Arduino IDE, via a type B USB cable. It can be powered by the USB cable or by an external 9-volt battery, though it accepts voltages between 7 and 20 volts. It is similar to the Arduino Nano and Leonardo. The hardware reference design is distributed under a Creative Commons Attribution Share-Alike 2.5 license and is available on the Arduino website. Layout and production files for some versions of the hardware are also available.

Arduino Nano

The Arduino Nano is a small, complete, and breadboard-friendly board based on the ATmega328P released in 2008. It offers the same connectivity and specs of the Arduino Uno board in a smaller form factor.

References

  1. "5 Steps for Selecting the Right USB to Serial adapter" . Retrieved 14 October 2012.
  2. "WCH CH340 USB UART chip" . Retrieved 11 December 2018.
  3. "Silicon Labs CP210x USB to UART Bridge VCP Drivers" . Retrieved 11 December 2018.
  4. "USB to UART/Serial/Printer". www.prolific.com.tw. Archived from the original on 7 March 2021. Retrieved 6 November 2021.
  5. "RS232 to USB converters" . Retrieved 14 October 2012.
  6. "FTDI Drivers" . Retrieved 14 October 2012.