View source for USB-to-serial adapter

{{more citations needed|date=October 2012}}
{{use dmy dates|date=July 2024|cs1-dates=y}}
[[File:FTDI USB SERIAL.jpg|thumb|right|[[FTDI]] US232R : [[USB]] to [[RS-232]] cable]]
A '''USB-to-serial adapter''' or simply '''USB adapter''' is a type of [[protocol converter]] that is used for converting [[USB]] data signals to and from [[serial communications]] standards ([[serial port]]s). Most commonly the USB data signals are converted to either [[RS-232]], [[RS-485]], [[RS-422]], or [[TTL serial|TTL-level]] [[UART]] serial data. The older serial [[RS-423]] protocol is rarely used any more, so USB to RS-423 adapters are less common.
== Uses ==
USB-to-serial RS-232 adapters are often used with consumer, commercial and industrial applications and USB-to-serial RS-485/422 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 protocol]]s 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 [[DE-9]] or [[DB-25]]) 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-coupler]]s 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 RS-232 port, also referred to as a COM port, which could be used for connecting the computer to most types of serial RS-232 devices. By the late 1990s, many computer manufacturers started to phase out the serial COM port in favor of the USB port (in part dictated from the [[PC97]] architecture, from [[Microsoft]]).
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 an RS-232, RS-485 or RS-422 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 ==
[[Image:PL2303HX-HD.jpg|thumb|[[Die (integrated circuit)|Die]] of a PL2303HX [[Universal Serial Bus|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 that 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.<ref>{{cite web |title=5 Steps for Selecting the Right USB to Serial adapter |url=http://www.usconverters.com/index.php?main_page=page&id=62&chapter=0 |access-date=14 October 2012}}</ref>
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 (Jiangsu Qin Heng) CH340,<ref>{{cite web |title=WCH CH340 USB UART chip |url=http://wch.cn/products/CH340.html|access-date=11 December 2018}}</ref> Silicon Labs 210x,<ref>{{cite web |title=Silicon Labs CP210x USB to UART Bridge VCP Drivers |url=https://www.silabs.com/products/interface/usb-bridges/classic-usb-bridges |access-date=11 December 2018}}</ref> Prolific PL2303<ref>{{cite web |title=USB to UART/Serial/Printer |url=http://www.prolific.com.tw/US/ShowProduct.aspx?pcid=41&showlevel=0017-0037-0041 |url-status=live |archive-url=https://web.archive.org/web/20210307195409/http://www.prolific.com.tw/US/ShowProduct.aspx?pcid=41&showlevel=0017-0037-0041 |archive-date=7 March 2021 |access-date=6 November 2021 |website=www.prolific.com.tw}}</ref>).
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 (engineering)|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.<ref>{{cite web |title=RS-232 to USB converters |url=http://www.lammertbies.nl/comm/info/RS-232-usb.html |access-date=14 October 2012}}</ref> Virtual COM drivers are usually available for Windows, Linux and Mac only.<ref>{{cite web |title=FTDI Drivers |url=http://www.ftdichip.com/FTDrivers.htm |access-date=14 October 2012}}</ref>
== References ==
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[[Category:USB]]
[[Category:Legacy hardware]]