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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 ports). Most commonly the USB data signals are converted to either RS-232, RS-485, RS-422, or 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.
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 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 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-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.
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.
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. [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 (Jiangsu Qin Heng) 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]
In telecommunications, RS-232 or 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 or PC, 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.
Transistor–transistor logic (TTL) is a logic family built from bipolar junction transistors. Its name signifies that transistors perform both the logic function and the amplifying function, as opposed to earlier resistor–transistor logic (RTL) and diode–transistor logic (DTL).
A universal asynchronous receiver-transmitter is a peripheral 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. Common signal levels are RS-232, RS-485, and raw TTL for short debugging links. Early teletypewriters used current loops.
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 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 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.
Data acquisition is the process of sampling signals that measure real-world physical conditions and converting the resulting samples into digital numeric values that can be manipulated by a computer. Data acquisition systems, abbreviated by the acronyms DAS,DAQ, or DAU, typically convert analog waveforms into digital values for processing. The components of data acquisition systems include:
GeoPort is a serial data system used on some models of the Apple Macintosh that could be externally clocked to run at a 2 megabit per second 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, also known as TIA/EIA-422, is a technical standard originated by the Electronic Industries Alliance, first issued in 1975, that specifies electrical characteristics of a digital signaling circuit. It was meant to be the foundation of a suite of standards that would replace the older RS-232C standard with standards 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 uses the same signaling systems but on a different wiring arrangement.
Serial Peripheral Interface (SPI) is a de facto standard for synchronous serial communication, used primarily in embedded systems for short-distance wired communication between integrated circuits.
1-Wire is a wired half-duplex serial bus designed by Dallas Semiconductor that provides low-speed (16.3 kbit/s) data communication and supply voltage over a single conductor.
RS-485, also known as TIA-485(-A) or EIA-485, is a standard, originally introduced in 1983, 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.
The RS-449 specification, also known as EIA-449 or TIA-449, defines the functional and mechanical characteristics of the interface between data terminal equipment, typically a computer, and data communications equipment, typically a modem or terminal server. The full title of the standard is EIA-449 General Purpose 37-Position and 9-Position Interface for Data Terminal Equipment and Data Circuit-Terminating Equipment Employing Serial Binary Data Interchange.
In computer engineering and electrical engineering, bit banging or bit bashing is a term of art for any method of data transmission that employs software as a substitute for dedicated hardware to generate transmitted signals or process received signals. Such software directly sets and samples the states of GPIOs to transmit and receive, respectively, 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.
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.
The Modified Modular Jack (MMJ) is a small form-factor serial port connector developed by Digital Equipment Corporation (DEC). It uses a modified version of the 6P6C modular connector with the latch displaced off-center so standard modular connectors found on Ethernet cables or phone jacks cannot accidentally be plugged in. MMJ connections are used on Digital minicomputers, such as the PDP-11, VAX and Alpha systems, and to connect terminals, printers, and serial console servers.
Universal EXTension (UEXT) is a connector layout which includes power and three serial buses: Asynchronous, I2C, and SPI separately over 10 pins in a 2x5 layout. The connector layout was specified by Olimex Ltd and declared an open-project that is royalty-free in 2011, and was used in all their boards after 2004.
The MAX232 is an integrated circuit by Maxim Integrated Products, now a subsidiary of Analog Devices, 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.
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.