What is 485 and what is 223

485 is an Arabic numeral, so is 223.

485 can be octal 223 can also be.

The 485 interface is also called AB line, which requires two wires, which are generally used for field wiring, and European terminals are generally used for the convenience of field wiring.

422 is also a field bus, different from 485, it requires 4 lines, you can understand that 485 is a half-duplex, that is, in the entire bus, only one person can not listen when he speaks, and Bi Wansui cannot speak when he listens.

This is called half-duplex.

422 is full-duplex, that is, when a person speaks, he can listen at the same time.

This is the difference between RS232 and RS485 in terms of communication capabilities.

In the case of RS232, it is mainly used for close device communication, and is not suitable for long-distance field communication. So the old-fashioned computers all have 232 interfaces. At that time, the 232 interface was mainly a card reader, a disk reader, and a kind of device.

Moreover, a buggy interface can only be connected to one device, that is, one-to-one communication. Instead of being like RS485, it can be one-to-many, which is called a bus. The RS232 has a maximum communication distance of only 15 meters.

As shown in the figure below. <>

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However, the on-board signal source of these three interfaces is a serial port, that is, a UART. So it can be easily converted to each other.

RS232 is also not suitable for large-scale networking in the field, because the RS232 line sequence needs to be connected to GND, so at least 3 lines are required to transmit signals. And RS485 is two lines.

However, it should be noted that many people are easily confused now, RS485 is said to be "AB line" and "two wires", but in fact, it needs additional power supply, that is, when networking, it actually needs four lines. Add two more power cords. Different from the popular "two buses", such as mbus, powerbus, etc., it is two lines that can communicate and supply power.

So two wires and two buses are still two concepts. Now when it comes to use, the convenience makes a big difference.

The RS485 is half-duplex and the RS422 is full-duplex. Quietly.

The RS422 has at least one differential transmit port and one differential receive port. When the two nodes are disturbed by the shed signal, the sending port of one side is connected to the receiving port of the other party, and two pairs of wires are required.

The differential transmitting port of RS485 is connected in parallel with its own differential receiving port, and only one pair of wires is required for RS485 to pass between multiple points.

RS422 cannot be used directly for direct interconnection of more than three electrics, and cannot be directly connected with a bus.

The RS-485 is connected by a bus, and the interface allows up to 128 transceivers to be connected on the bus (with multi-station capability).

The 485 protocol refers to the RS-485 protocol, which is a standard for serial communication. Typical serial communication standards are RS232 and RS485, which define voltage and impedance, but not software protocols. The RS-485 bus standard specifies the criteria for the electrical characteristics of the bus interface, i.e., the definition of two logical states:

The positive level is between +2V and +6V, indicating a logical state; A negative level between -2V and -6V indicates another logical state; The digital signal adopts differential transmission mode, which can effectively reduce the interference of noise signal. Typical serial communication standards are RS232 and RS485, which define voltage, impedance, etc. , but does not define a software protocol.

Characteristics that differ from RS232 and RS485 include: electrical characteristics: logic "1" is represented by a voltage difference between the two wires of +(2-6) V; The logic "0" is represented by the voltage difference between the two lines as -(2-6) V, and the interface signal level is lower than that of RS-232-C, so it is not easy to damage the chip of the interface circuit, and this level is also the TTL level, which can be easily connected to the TTL circuit.

The highest data transmission rate is strong interface, that is, it is good against noise interference. The standard value of the maximum transmission distance of the interface is 4000 feet, and the actual distance can reach 3000 meters (in theory, the actual limit distance is only about 1200 meters). In addition, the RS-232-C interface allows only one transceiver to be connected on the bus, i.e. single-station capability.

The RS-485 interface allows up to 128 transceivers to be connected to the bus. This means that it has multi-station capability, allowing users to easily set up a network of devices using a single RS-485 interface. The RS-485 interface is the serial interface of choice due to its good immunity to noise interference, long transmission distance, and multi-station capability.

Since the half-duplex network composed of RS485 interfaces generally only needs two wires, Suifan uses shielded twisted pair cables to transmit all RS485 interfaces. The 9-pin plug and socket of the DB-9 is used for the RS485 interface connector, the DB-9 (hole) is used for the RS485 interface with the smart terminal, and the DB-9 (pin) is used for the RS485 keyboard interface connected to the keyboard.

485 Typical serial communication standards are RS232 and Yanxiao RS485, which define voltage, impedance, etc., but do not define software protocols, and unlike RS232, RS485 features include:

1.The electrical characteristics of RS-485: the logic "1" is represented by the voltage difference between the two wires as +(2-6)v; The logic "0" is expressed as the voltage difference between the two wires as -(2-6)v.

The signal level of the receiver port is lower than that of RS-232-C, so it is not easy to damage the chip of the interface circuit, and the level is compatible with the TTL level, which can be easily connected to the TTL circuit.

2.The RS-485 has a maximum data transfer rate of 10Mbps.

3.The RS-485 interface is a combination of balanced driver and differential receiver, and the anti-common-mode interference ability is enhanced, that is, the anti-noise interference is good.

4.The RS-485 interface has a maximum transmission distance of 4000 feet as standard, but in practice it can reach 3000 meters, and the RS-232-C interface allows only one transceiver to be connected on the bus, i.e. single-station capability. The RS-485 interface on the bus allows up to 128 transceivers to be connected.

This means that it has multi-station capability, so that users can easily set up a network of devices with a single RS-485 interface.

The MAX485 is a type of chip interface.

The MAX485 interface chip is an RS 485 chip from Maxim.

It operates from a single power supply of +5 V, with a rated current of 300 A, and adopts a half-duplex communication mode. It completes the function of converting TTL level to RS 485 level. The MAX485 chip has a very simple structure and pins, and contains a driver and receiver inside.

The RO and DI terminals are respectively the output of the receiver and the input of the driver, and only need to be connected with the RXD and TXD of the single-chip microcomputer respectively when connected with the single-chip microcomputer; The RE and DE terminals are the enable terminals of receive and transmit respectively, and when RE is logic 0, the device is in the receive state; When DE is logic 1, the device is in the transmit state, because the MAX485 operates in a half-duplex state, so only one pin of the microcontroller needs to control these two pins; The A and B terminals are the differential signal terminals for receiving and transmitting, respectively, and when the level of the A pin is higher than B, it means that the transmitted data is 1; When the level of A is lower than that of B, the data sent is 0. The wiring is very simple when connected with a microcontroller. Only one signal is required to control the reception and transmission of the MAX485.

At the same time, a matching resistor is added between a and B terminals, and a resistor of 100 can generally be selected.

It can draw power from the serial port and drive the MAX232 to communicate with the MAX485. When the load is not added, the voltage is there, and the voltage is reduced by about 3V after the load is added.

It's RS485, it's a level interface, the transmission distance is long, I have this kind of module.

The 485 communication protocol is the standard for serial communication. Voltage, impedance, etc., are defined, but software protocols are not defined.

2.The bus standard specifies the standard for the electrical characteristics of the bus interface, i.e. the definition of 2 logical states: a positive level between +2V and +6V, indicating a logical state.

3.If the negative level is between -2V and -6V, it indicates another logical state; The digital signal adopts the differential transmission mode, which can effectively reduce the interference of the noisy signal. The 485 industrial bus standard can effectively support multiple sub-nodes and has the characteristics of long communication distance and high sensitivity to information reception.

The difference between rs232 and rs485.

It is a serial physical interface standard developed by the Electronic Industry Association (EIA). RS is the abbreviation of "recommended standard", 232 is the identification number, and C indicates the number of modifications. The RS-232-C bus standard has 25 signal lines, including one main channel and one auxiliary channel, and in most cases the main channel is mainly used, and for general duplex communication, only a few signal lines are required, such as a transmit line, a receive line, and a ground wire.

The RS-232-C standard specifies a data transfer rate of baud per second. The RS-232-C standard specifies that the driver is allowed to have a capacitive load of 2500pf, and the communication distance will be limited by this capacitance, for example, when using a 150pf m communication cable, the maximum communication distance is 15m; If the capacitance per meter of cable decreases, the communication distance can be increased. Another reason for the short transmission distance is that RS-232 is a single-ended signal transmission, which has problems such as common ground noise and cannot suppress common mode interference, so it is generally used for communication within 20 meters.

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

The RS-485 operates in a half-duplex mode, and only one point can be transmitted at any one time, so the transmit circuit must be controlled by an enable signal. The RS-485 is very convenient for multi-point interconnection, which can eliminate many signal lines. The RS-485 can be networked to form a distributed system, which allows up to 32 drivers and 32 receivers to be connected in parallel.

Fei Najin, 232 full duplex features: several degrees fast. Disadvantages: poor anti-interference.

485 half-duplex feature: anti-interference. Disadvantages: low degree.