Differences Between RS232 and RS485 ports)

Differences Between RS232 and RS485

1. RS-232-C is a serial physical interface standard developed by the American Association of Electronic Industry EIA (Electronic Industry Association. RS is the abbreviation of the English "Recommendation Standard". 232 indicates the ID number, and C indicates the number of modifications. RS-232-C bus standard has 25 signal lines, including a main channel and a secondary channel, in most cases the main channel, for general duplex communication, only a few signal lines can be achieved, such as a sending line, a receiving line, and a ground line. The RS-232-C standard sets the data transmission rate per second 50, 75, 100, 150, 300, 600, 1200, 2400, 4800, 9600 port. RS-232-C standards stipulate that the drive can have pf capacitive load, the communication distance will be limited by this capacitance, for example, when using a 150pf/M communication cable, the maximum communication distance is 15 m; if the electrical capacity of each meter is reduced, the communication distance can be increased. Another reason for short transmission distance is that the RS-232 is a single-ended signal transmission, there are common noise and can not suppress common mode interference and other problems, so it is generally used for communications within 20 m.

2. RS-485 bus, widely used in RS-485 serial bus standard when the communication distance is dozens of meters to kilometers. The RS-485 adopts balanced transmission and differential reception, so it has the ability to suppress common mode interference. In addition, the bus transceiver is highly sensitive and can detect voltage as low as 200mV. Therefore, the transmission signal can be recovered from kilometers away. RS-485 uses half duplex mode, at any time only a little in the sending State, therefore, the sending circuit must be controlled by the enabling signal. RS-485 for Multi-Point interconnection is very convenient, can save a lot of signal lines. The application RS-485 can be networked to form a distributed system that allows up to 32 drivers and 32 receivers in parallel.

in the past, communication between PCs and smart devices mostly relies on RS232, RS485, and Ethernet, depending on the interface specifications of devices. However, RS232 and RS485 can only represent the communication physical media layer and link layer. To achieve bidirectional data access, you must write your own Program for communication applications. However, most of these programs do not comply with ISO/OSI specifications and can only implement a single function, applicable to a single device type, and the program is not universal. In a device network connected by RS232 or RS485 devices, if the number of devices exceeds 2, RS485 must be used as the communication medium. To connect devices on the RS485 network, only the master) this is usually a PC. In this case, only one master device is allowed in the network, and all others are slave devices. The fieldbus technology is based on the ISO/OSI model and has a complete software support system, which can solve problems such as bus control, conflict detection, and link maintenance.