What is the difference between RS 232 and RS 485?

1、rs-232-c

RS-232-C 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 primary channel and one auxiliary channel.

In most cases, the main channel is 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.

2、rs-485

RS-485 bus, when the communication distance is required to be tens of meters to thousands of meters, the RS-485 serial bus 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.

The differences between RS232 and RS485 are as follows:

1. The transmission mode is different.

The RS232 uses an unbalanced transmission method, the so-called single-ended transmission. RS485 adopts balanced transmission, that is, differential transmission mode.

The RS232 transmitter outputs a positive level of 5 15V, a negative level of -5 -15V, TTL on the line when there is no data, and the receiver works at 3 12V and -3 -12V. Poor common-mode rejection.

Between RS485AB, the positive point level is +2 +6V, and the negative level is -2 -6. A receiver AB greater than +200mV is a positive logic level, and less than -200mV is a negative logic level.

2. The transmission distance is different.

The RS232 is suitable for transmission between local devices with a maximum transmission distance of 15 meters. The RS485 transmission distance is tens of meters to thousands of meters.

3. RS232 only allows one-to-one communication, is full-duplex, and can send and receive at the same time. The RS485 interface allows 128 transceivers to be linked on the bus, which is half-duplex, and one can only receive or receive.

4. The transmission rate is different.

The RS232 has a maximum rate of 20kB and a transmission rate of up to 10M.

<> wiring diagram. The network structure is differentRS232 is a 1:1 communication, i.e. one-to-one.

RS485 is a 1:n communication method, i.e. one-to-many. The RS485 interface allows up to 128 transceivers to be connected on the bus, one of which acts as a master and the others as slaves, and multiple slaves are distinguished by address codes.

1. To put it simply, RS232 is full-duplex, RS485 is half-duplex, and RS422 is full-duplex.

2. The data transmission rate specified in the RS-232-C standard is baud.

3. The maximum data transmission rate of RS-485 is 10Mbps, and the maximum communication distance is about 1219M, and the transmission rate is inversely proportional to the transmission distance.

4. However, because RS-485 often has to communicate with the RS-232 port of the PC, it is actually the highest. And because the rate is too high, the transmission distance of RS-485 will be reduced, so it is often about 9600bps or below.

5. The maximum transmission distance of RS-422 is 4000 feet (about 1219 meters), and the maximum transmission rate is 10MB s. The length of the balanced twisted pair is inversely proportional to the transmission rate, and the maximum transmission distance can only be reached when the rate is less than 100kbs.

6. The highest rate transmission can only be obtained at a very short distance. The maximum transfer rate that can be obtained on a 100-meter-long twisted pair cable is only 1MB s.