By the late '90s, many computer manufacturers started to phase out the serial COM port in favor of the USB port.
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. 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. 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. USB serial adapters can be isolated or non-isolated. 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.
Currently, USB to TTL-level UART converters are used extensively by students and hobbyist as they can be directly interfaced to microcontrollers.Īdapters for converting USB to other standard or proprietary protocols also exist however, these are usually not referred to as a serial adapter. USB to serial RS232 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. The older serial RS423 protocol is rarely used any more, so USB to RS423 adapters are less common. Most commonly the USB data signals are converted to either RS-232, RS-485, RS-422, or TTL-level UART serial data. 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).
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