StarTech.com 1 Port USB to Serial RS232 Adapter - Prolific PL-2303 - USB to DB9 Serial Adapter Cable - RS232 Serial Converter (ICUSB232V2)

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The reason behind this variation in implementation of the RS232 standard is that not all devices and applications require the full specifications and functionality of the RS232 Protocol. For example, a serial Modem using RS232 may require more control lines than a serial Mouse using serial port. Yes, a RS232 to USB converter does have a full-blown UART circuit built-in. As any standard UART, it does have Rx, Tx, and flow control pins. As any UART, it must be properly configured to be able to communicate with the "partner" at the other end of UART link.

Microcontrollers don’t tolerate RS232 voltages and may be damaged. To avoid this, UART (Universal Asynchronous Transmitter Receiver) is used. It sends and receives the data in serial form. To do the level conversion of voltages, RS232 driver IC such as MAX232 is used between the UART and serial port. RS232 – UART Advantages

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Serial ports rely on a microcontroller chip called a Universal Asynchronous Receiver Transmitter (UART) to "serialize" the data coming from the host computer's bus so it can be transmitted through the serial port. Serializing means transforming bytes of data into a sequence of bits with start and stop bits on either end. On the receiving end, another UART chip reconverts the serialized data into "parallel" bytes. Most UART chips cache data coming in from the computer bus so they can transmit faster than the normal 115 Kbps transmission rate of a standard serial port. RS232 has become a de facto standard for computer and instrumentation devices since it was standardised in the year 1962 by EIA and as a result, it became the most widely used communication standard.

RS232 was introduced in 1960’s and was originally known as EIA Recommended Standard 232. RS232 is one of the oldest serial communication standards with ensured simple connectivity and compatibility across different manufacturers. Originally, the DTEs in RS32 are electromechanical typewriters and DCEs are modems.

The signal voltage between +3V to +25V represents logic ‘1’ and the signal voltages between -3V to -25V represents logic ‘0’. Whereas the control voltage signals use negative logic, i.e., logic ‘1’ indicates -3 to -25 volts and logic ‘0’ indicates +3V to +25V. The voltage from -3V to +3V is considered as an indeterminate state. During asynchronous communication, both RTS and CTS are on all the way through the session. Yet, if DTE is connected to a multipoint line, data is transmitted by one station at a time (due to the return phone pair sharing), so the only use for RTS is to turn the modem’s carrier on and off. A station raises RTS when it’s ready to transmit. The modem turns on its carrier, waits until it’s stabilized (normally it takes a couple of milliseconds), and raises CTS. While CTS is up, DTE transmits. Once the transmission is finished, the station drops RTS and then the modem drops both CTS and carrier.