What Is an RS 232 Transceiver?

The RS-232 standard interface (also known as EIA RS-232) is one of the commonly used serial communication interface standards. Formulated, its full name is "Technical Standard for Serial Binary Data Exchange Interface Between Data Terminal Equipment (DTE) and Data Communication Equipment (DCE)". ^[1]

In serial communication, both parties of the communication are required to use a standard interface, so that different devices can be easily connected for communication. RS-232-C

(1) The signal level of the interface is high, and it is easy to damage the interface circuit.

The following explains the principle of RS-232 serial communication with the communication flow between the computer and the modem. Consider the interaction and working process between the RS-232 signal between the computer and the modem when the modem is in the answer mode. Assumes that the modem is full duplex and uses RS-232
Standards work. ^[4]

RS-232 and USB are serial communication, but no matter it is the underlying signal, level definition, mechanical connection method, data format, communication protocol, etc., the two are completely different. RS-232 is a popular interface. In MS-DOS, the four serial interfaces are called COM1, COM2, COM3, and COM4, and most windows applications can have up to 4 peripherals, but if users want to expand more peripherals, they must Use plug-in serial card or external switch box. RS-232 point-to-point connection, one serial port can only connect one peripheral. ^[5]

And USB is a kind of multi-point, high-speed connection method, using a hub can achieve more connections. The basic part of the USB interface is the serial interface engine SIE. The SIE receives data bits from the USB transceiver, converts them into valid bytes, and transmits them to the SIE interface. Conversely, the SIE interface can also receive bytes and convert them into serial bits to the bus. As the maximum speed of the PC serial port is only 115.2kbps, a speed bottleneck will be formed. The RS-232 system includes two serial signal paths with opposite directions for transmitting commands and data respectively, and the commands and status must be interleaved with the data; while USB supports separate command and data channels and allows independent status reporting . USB is a convenient, flexible, simple, high-speed bus structure. Compared with the traditional RS-232 interface, USB has the following characteristics: ^[5]

(1) USB uses a single form of connector and connection cable to achieve a single data universal interface. USB unified 4-pin plug replaces a wide variety of serial / parallel plugs behind the PC case, and realizes the unification of conventional I / O devices, multimedia devices (parts), communication devices (phones, networks) and household appliances into one type Interface wishes. ^[5]

(2) USB uses a tree structure that is easy to expand. By using USB Hub expansion, up to 127 peripherals can be connected. USB exempts all system resource requirements, avoids the problem of port conflicts when installing hardware, and frees up hardware resources for other devices. ^[5]

(3) USB peripherals can be set automatically, supporting plug and play and hot plugging. ^[5]

(4) Flexible power supply. The USB cable has the function of transmitting power, supports energy saving mode, and low power consumption. The USB bus can provide a power supply with a voltage of + 5v and a maximum current of 500mA, which is used as a power source for low-power-consumption devices, and does not require additional power. ^[5]

(5) USB can support four transmission modes: control transmission, synchronous transmission, interrupt transmission, and batch transmission, which can be applied to many types of peripherals.

(6) The communication speed is fast. USB supports three bus speeds, low speed 1.5Mbps, full speed 12Mbps and high speed 480Mbps. ^[5]

(7) Reliability of data transmission. USB adopts differential transmission mode, and has error detection and correction functions to ensure the correct transmission of data. ^[5]

(8) Low cost. USB simplifies the connection and configuration of peripherals, effectively reduces the overall cost of the system, is a cheap, simple and practical solution, and has a high performance-price ratio. ^[5]

RS-232 has a wide range of applications, is cheap, is easy to program, and can use longer wires than other interfaces. As USB ports become more common, more USB-to-RS-232 or other interfaces will appear. Conversion device. But RS-232 and similar interfaces will still find widespread use in applications such as monitoring and control systems. For developers and products accustomed to using RS-232, you can consider designing a USB / RS-232 converter to transmit RS-232 data through the USB bus, that is, the application software on the PC side is still programmed for the RS-232 serial port, and peripherals RS-232 is also used as the data communication channel, but the physical connection from the PC to the peripherals is the USB bus, and the data communication on it is also the USB data format. The advantages of this method are: on the one hand, to protect the original software development investment, and the application software that has been successfully developed for RS-232 peripherals can continue to be used without modification; on the other hand, the advantages of the USB bus are fully utilized. More RS-232 devices can be connected through the USB interface, which not only can obtain higher transmission speed and achieve true plug and play, but also solves the disadvantage that the USB interface cannot transmit over long distances (USB communication distance is within 5 meters. ^{[ 5]}