What interface is ioioi?

ioioi refers to the COM interface, that is, the serial communication port, referred to as the serial port, which is an expansion interface that uses serial communication. The COM interface refers to the sequential transmission of data bit by bit; its characteristic is that the communication line is simple, and only a pair of transmission lines can achieve two-way communication (the telephone line can be directly used as the transmission line), thus greatly reducing the cost, and is especially suitable for long distances Communication, but transfer speed is slower.

The operating environment of this tutorial: Windows 7 system, Dell G3 computer.

The IOIO interface on the PC is actually the COM interface, which refers to the cluster communication port interface, that is, the serial communication port, commonly known as the serial port; it is an expansion interface that uses serial communication.

#COM interface refers to the sequential transmission of data bit by bit. Its characteristic is that the communication line is simple, and only a pair of transmission lines can achieve two-way communication (telephone lines can be directly used as transmission lines), thus greatly reducing costs, and is especially suitable for long-distance communication, but the transmission speed is slow.

The communication method in which each bit of data of a message is transmitted bit by bit in sequence is called serial communication. The characteristics of serial communication are: the transmission of data bits is carried out in bit order and can be completed with at least one transmission line; the cost is low but the transmission speed is slow. The distance of serial communication can range from a few meters to several kilometers; according to the direction of information transmission, serial communication can be further divided into three types: simplex, half-duplex and full-duplex.

The origin of the serial port

The serial port appeared around 1980, and the data transmission rate is 115kbps~230kbps. The initial appearance of serial ports was for the purpose of connecting computer peripherals. In the early days, serial ports were generally used to connect devices such as mice and external modems, as well as old-fashioned cameras and writing pads. Serial ports can also be used for interconnection and data transmission between two computers (or devices). Since the serial port (COM) does not support hot swapping and has a low transmission rate, some new motherboards and most portable computers have begun to cancel this interface. Serial ports are mostly used in industrial control and measurement equipment and some communication equipment.

Interface classification standard

Synchronous Serial Interface (English: Synchronous Serial Interface, SSI) is a commonly used industrial communication interface.

Asynchronous serial refers to UART (Universal Asynchronous Receiver/Transmitter), universal asynchronous reception/transmission. UART is a chip that converts parallel input into serial output, usually integrated on the motherboard. UART includes TTL level serial port and RS232 level serial port. The TTL level is 3.3V, while RS232 is a negative logic level. It defines 5~12V as low level, and -12~-5V as high level. MDS2710, MDS SD4, EL805, etc. are RS232 interfaces. EL806 has TTL interface.

Serial interfaces are classified according to electrical standards and protocols, including RS-232-C, RS-422, RS485, etc. The RS-232-C, RS-422 and RS-485 standards only specify the electrical characteristics of the interface and do not involve connectors, cables or protocols.

• RS-232

Also known as the standard serial port, it is the most commonly used serial communication interface. It is a standard for serial communications developed in 1970 by the Electronic Industries Association (EIA) in conjunction with the Bell System, modem manufacturers and computer terminal manufacturers. Its full name is "Technical Standard for Serial Binary Data Exchange Interface between Data Terminal Equipment (DTE) and Data Communications Equipment (DCE)". The traditional RS-232-C interface standard has 22 wires and uses a standard 25-pin D-type plug socket (DB25). Later, it was simplified to a 9-pin D-type socket (DB9). The 25-pin plug socket is rarely used in current applications. .

RS-232 adopts unbalanced transmission method, which is the so-called single-ended communication. Since the difference between its sending level and receiving level is only about 2V to 3V, its common mode suppression capability is poor. Coupled with the distributed capacitance on the twisted pair, the maximum transmission distance is about 15 meters and the maximum rate is 20kb. /s. RS-232 is designed for point-to-point (that is, only one pair of receiving and transmitting devices) communication, and its driver load is 3~7kΩ. So RS-232 is suitable for communication between local devices.

• RS-422

The full name of the standard is "Electrical Characteristics of Balanced Voltage Digital Interface Circuits", which defines the characteristics of the interface circuit. A typical RS-422 is a four-wire interface. There is actually a signal ground wire, a total of 5 wires. Its DB9 connector pin definition. Since the receiver uses high input impedance and the transmit driver has stronger driving capability than RS232, it allows multiple receiving nodes to be connected on the same transmission line, up to 10 nodes. That is, there is one master device (Master) and the rest are slave devices (Slave). The slave devices cannot communicate with each other, so RS-422 supports point-to-many two-way communication. The input impedance of the receiver is 4k, so the maximum load capacity of the transmitter is 10×4k 100Ω (terminating resistor). Since the RS-422 four-wire interface uses separate sending and receiving channels, there is no need to control the data direction. Any necessary signal exchanges between devices can be performed in software (XON/XOFF handshake) or hardware (a pair of separate pairs of Stranded wire) implementation.

The maximum transmission distance of RS-422 is 1219 meters, and the maximum transmission rate is 10Mb/s. The length of its balanced twisted pair is inversely proportional to the transmission rate. The maximum transmission distance can only be achieved below a rate of 100kb/s. The highest transmission rates are only achieved over very short distances. Generally, the maximum transmission rate that can be obtained on a 100-meter-long twisted pair is only 1Mb/s.

• RS-485

is developed based on RS-422, so many electrical regulations of RS-485 are different from those of RS-422 similar. If all use balanced transmission methods, they all need to connect terminating resistors on the transmission lines. RS-485 can use two-wire and four-wire methods. The two-wire system can achieve true multi-point two-way communication. When using a four-wire connection, like RS-422, it can only achieve point-to-many communication, that is, there can only be one master ( Master) device, and the rest are slave devices, but it is improved over RS-422. No matter the four-wire or two-wire connection method, 32 more devices can be connected to the bus.

The difference between RS-485 and RS-422 is that their common mode output voltage is different. RS-485 is between -7V and 12V, while RS-422 is between -7V and 7V. RS The minimum input impedance of the -485 receiver is 12kΩ and RS-422 is 4kΩ; since RS-485 meets all RS-422 specifications, the RS-485 driver can be used in the RS-422 network.

RS-485 is the same as RS-422, its maximum transmission distance is about 1219 meters, and its maximum transmission rate is 10Mb/s. The length of the balanced twisted pair is inversely proportional to the transmission rate. Only when the rate is below 100kb/s can the longest specified cable length be used. The highest transmission rates are only achieved over very short distances. Generally, the maximum transmission rate of a 100-meter twisted pair is only 1Mb/s.

The difference between serial port and parallel port

The serial port can be described as one lane, while the parallel port has 8 lanes and can transmit 8 lanes at the same time. bit (one byte) of data. But this does not mean that the parallel port is fast. Due to the mutual interference (crosstalk) between 8-bit channels, the transmission speed is limited and the transmission is prone to errors. The serial ports do not interfere with each other. The amount of data sent simultaneously by the parallel port is large, but it is slower than the serial port. This is how serial hard drives are valued by people.

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