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232接口芯片ichaiyang 2024-05-10 5:48 20
The RS-232 interface conforms to the serial data communication interface standard developed by the American Electronic Industry Alliance (EIA , and the original number is the full...

RS232 RS422 RS485 definition and difference, there are no detailed points. Thank you?

The RS-232 interface conforms to the serial data communication interface standard developed by the American Electronic Industry Alliance (EIA), and the original number is the full name of EIA-RS-232 (referred to as 232, RS232). It is widely used in computer serial interface peripheral connection. Connecting cables and mechanical, electrical characteristics, signal functions and transmission processes.

The RS-232-C standard specifies data transfer rates of 50, 75, 100, 150, 300, 600, 1200, 2400, 4800, 9600, 19200 baud per second.

RS232 Features:

RS-232 is one of the mainstream serial communication interfaces. Due to the earlier appearance of the RS232 interface standard, there are inevitably shortcomings, mainly the following four points:

(1) The signal level value of the interface is high, which is easy to damage the chip of the interface circuit. The voltage of any signal line on the RS232 interface is negative logic. That is, logic \"1\" is -3 -- 15V; Logic \"0\" : 3-15V, noise tolerance is 2V. That is, the receiver is required to recognize a signal higher than 3V as a logical \"0\

(2) The transmission rate is low, in the asynchronous transmission, the bit rate is 20Kbps; Therefore, in the 51CPLD development board, the comprehensive program baud rate can only be used 19200, which is also the reason.

(3) The interface uses a signal line and a signal return line to form a common ground transmission form, which is easy to produce common mode interference, so the anti-noise interference is weak.

(4) The transmission distance is limited, the maximum transmission distance standard value is 50 feet, in fact, it can only be used at about 15 meters.

RS485 Overview

When the communication distance is required to be tens of meters to thousands of meters, RS-485 serial bus is widely used. RS-485 uses balanced transmission and differential reception, so it has the ability to suppress common-mode interference. Coupled with the high sensitivity of the bus transceiver, it can detect voltages as low as 200mV, so the transmitted signal can be recovered from kilometers away.

RS-485 uses half duplex mode of operation, only one point at any time is in the sending state, so the sending circuit must be controlled by the enable signal.

RS485 Features:

RS-485 is very convenient when used for multi-point interconnection and can eliminate many signal lines. The application RS-485 can be networked to form a distributed system that allows up to 32 drivers and 32 receivers to be connected in parallel. In view of the shortcomings of RS-232-C, the new standard RS-485 has the following characteristics:

(1) Electrical characteristics of RS-485: logic \"1\" is expressed by the voltage difference between the two lines 2V~ 6V, logic \"0\" is expressed by the voltage difference between the two lines -6V~-2V. The interface signal level is lower than RS-232-C, it is not easy to damage the interface circuit chip, and the level is compatible with TTL level, and it is convenient to connect with TTL circuit.

(2) Maximum data transmission rate: 10Mbps

(3) RS-485 interface adopts the combination of balanced driver and differential receiver, which has strong resistance to common mode interference, that is, good anti-noise performance.

(4) The maximum transmission distance of the RS-485 interface is 4000 feet, which can actually reach 3000 meters.

(5) The RS-232-C interface allows only one transceiver to be connected on the bus, that is, single-station capability; The RS-485 interface only allows the connection of up to 128 transceivers on the bus, that is, it has multi-station capability, so that users can use a single RS-485 interface to easily establish a device network.

Overview of RS422

The full name of the RS-422 standard is \"Electrical Characteristics of Balanced voltage digital interface circuits\

The principle of RS-422 and RS-485 circuits is basically the same, both send and receive in a differential manner, without the need for a digital ground wire. Differential work is the fundamental reason for the long transmission distance under the same rate condition, which is the fundamental difference between the two and RS232, because RS232 is a single-ended input and output, and at least a digital ground wire is required when working in duplex. The sending line and the receiving line are three lines (asynchronous transmission), and other control lines can be added to complete synchronization and other functions.

RS-422 can work in full duplex through two pairs of twisted pairs without affecting each other, and RS485 can only work in half duplex, sending and receiving can not be carried out at the same time, but it only needs a pair of twisted pairs. RS422 and RS485 can transmit 1200 meters at 19kpbs. The device can be connected on the line with the new transceiver.

The electrical properties of the RS-422 are identical to those of the RS-485. The main difference is that the RS-422 has four signal lines: two transmit (Y, Z) and two receive (A, B). Since RS-422 receives and sends separately, it can receive and send at the same time (full duplex); RS-485 has two signal lines: transmit and receive.

RS422 Features:

The RS-422 four-wire interface uses separate transmit and receive channels, so it does not need to control the direction of the data, and any necessary signal exchange between the devices can be in software mode (XON\/XOFF handshake) or hardware mode (a separate pair of twisted pairs). The RS-422 has a maximum transmission range of 4,000 feet (about 1,219 meters) and a maximum transmission rate of 10Mb\/s. The length of the balanced twisted pair is inversely proportional to the transmission rate, and the maximum transmission distance is possible only when the rate is below 100kb\/s. Only over very short distances can the highest transmission rates be obtained. Generally, the maximum transmission rate that can be obtained on a 100-meter-long twisted pair is only 1Mb\/s.

RS-422 requires a final resistance that is approximately equal to the characteristic impedance of the transmission cable. No final resistance is required for short distance transmission, that is, no final resistance is generally required below 300 meters. The terminal resistor is connected to the farthest end of the transmission cable.

The difference between RS-232\/RS-422\/RS-485

1, RS232 is full duplex, RS485 is half duplex, RS422 is full duplex.

2, RS485 and RS232 is only the physical protocol of communication (that is, the interface standard) there is a difference, RS485 is a differential transmission mode, RS232 is a single-ended transmission mode, but the communication program is not too much difference.

PC has been equipped with RS232, direct use on the line, if the use of RS485 communication, as long as the RS232 port with a RS232 to RS485 converter head can be, do not need to modify the program.

Is there a difference in the appearance of RS232, RS422, or RS485 ports?

Generally, it is DB9, there are others, or you have to look at the line inside to know what kind of rs232rs422rs485.

RS232 is a standard interface, D-shaped 9-needle, the signal definition of the interface of the connected device is the same, and its signal definition is as follows:

RS-232 allows one-to-one communication only (single station capability)

RS-485 interface allows connection of up to 128 transceivers on the bus (with multi-station capability)

Since the PC has only RS232 interface by default, there are two ways to get the RS485 circuit of the PC host computer:

(1) The PC serial port RS232 signal is converted into RS485 signal through RS232\/RS485 conversion circuit, and it is best to choose products with anti-surge zone isolation for complex industrial environments.

(2) Through PCI multi-serial card, you can directly choose the output signal of RS485 type expansion card.

Through RS232-RS485 converter, the computer is successively connected to multiple 485 devices (access controllers), and the devices on the bus are communicated in turn by polling.

The connection mark is 485 485-, corresponding to 485 485- of the linked device (controller).

Communication distance: the theoretical distance between the farthest device (controller) and the computer is 1200 meters, it is recommended that customers control within 800 meters, and the best effect can be controlled within 300 meters. If the distance is too long, you can buy 485 repeater (extender) (please buy from a professional converter production company, the position of the repeater is in the middle of the bus or the beginning, please refer to the relevant manufacturer's instructions.) Optional Repeaters can theoretically be extended up to 3,000 meters.

Load quantity: That is, a 485 bus can take how many devices (controller), this depends on the controller of the communication chip and 485 converter of the communication chip selection, there are generally 32, 64, 128, 256 several choices, this is the theoretical number, practical application, according to the field environment, communication distance and other factors, the number of loads can not reach the index number. Microcultivator controllers and converters are designed according to 256 units, and it is actually recommended that customers control each bus within 80 units.

485 communication bus (must use twisted pair, or one of the network cable), if the use of ordinary wire (no twisted-pair) interference will be very large, communication is not smooth, or even communication.

Each controller device must be strung hand in hand, and there can be no star connections or forks. If there is a star connection or bifurcation, the interference will be very large, poor communication, or even no communication.