Video conference camera RS232/RS485/RS422 control interface are serial port standard, serial port is also called serial interface, also known as serial communication interface, according to electrical standards and protocols to include RS-232-C, RS-422, RS485, USB and so on. The RS-232-C, RS-422, and RS-485 standards only specify the electrical characteristics of the interface, not the connectors, cables, or protocols. USB is a new interface standard developed in recent years, which is mainly used in the field of high-speed data transmission.
Video conferencing camera serial interface
RS-232 control interface
RS-232 is a serial physical interface standard developed by the Electronic Industry Association (EIA). RS is the abbreviation of “recommended standard” in English, and 232 is the identification number. The RS-232 bus standard has 25 signal lines, including a primary channel and a secondary channel.
In most cases, the main channel is mainly used. For general duplex communication, only a few signal lines are needed, such as a sending line, a receiving line and a ground line. The data transmission rate specified by the RS-232-C standard is 50, 75, 100, 150, 300, 600, 1200, 2400, 4800, 9600, 19200 baud per second.
The RS-232-C standard stipulates that the driver is allowed to have a 2500pF capacitive load, and the communication distance will be limited by this capacitance. For example, the maximum communication distance is 15m when a 150pF/m communication cable is used. If the capacitance per meter of cable is reduced, 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 20m.
Serial interface male and female head
RS-485 control interface
RS-485 bus, when the communication distance is required for 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. In addition, the bus transceiver is highly sensitive and can detect voltages as low as 200mV, so the transmitted signal can be recovered from kilometers away. RS-485 adopts half-duplex working mode, and only one point can be in the transmitting state at any time. Therefore, the transmitting circuit must be controlled by the enabling signal.
RS-485 is very convenient for multi-point interconnection, which can save many signal lines. The application of RS-485 can be networked to form a distributed system, which allows up to 32 drivers and 32 receivers in parallel.
Performance comparison between RS-232 and RS-485
RS485 interface is a combination of balanced driver and differential receiver, good anti-noise interference. RS232 interface uses a signal line and a signal return line to form a common ground transmission form, this common ground transmission is easy to produce common mode interference.
2. Transmission distance
The standard maximum transmission distance of RS485 interface is 1200 meters (9600bps), but it can actually reach 3000 meters. RS232 transmission distance is limited, the maximum transmission distance standard value is 50 meters, in fact, can only be used in about 15 meters.
3. Communication capability
The RS-485 interface allows up to 128 transceivers to be connected on the bus. Users can easily establish a device network using a single RS-485 interface. RS-232 only allows one-to-one communication.
4. Transmission rate
RS-232 has a low transmission rate, with a baud rate of 20Kbps during asynchronous transmission. The maximum data transfer rate of RS-485 is 10Mbps.
5. Signal line
The half-duplex network composed of RS485 interface generally only needs two signal lines. RS-232 generally only uses RXD, TXD, and GND lines.
6. Electrical level value
The logic “1” of RS-485 is represented by the voltage difference between the two lines as + (2-6) V; Logic “0” is shown by the voltage difference between the two lines as – (2-6) V. The voltage of any signal line in RS-232-C is negative logic relationship. Namely: logic “1”, -5- -15V; Logic “0 “+5- +15V.
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USB3.0 acquisition card /USB3.0 coding control board
RS-4222 control interface
RS422 bus,RS485 and RS422 circuit principle is basically the same, are sent and received in differential mode, do not need digital ground wire.
Differential work is the fundamental reason for the long transmission distance under the condition of the same rate, which is the fundamental difference between the two and RS232, because RS232 is single-ended input and output, at least digital ground wire is required for duplex work. Sending line and receiving line three lines (asynchronous transmission), but also can add other control lines to complete the synchronization and other functions, RS422 through two pairs of twisted pair can be full duplex work transceiver does not affect each other, and RS485 can only half duplex work, sending and receiving can not be carried out at the same time, but it only needs a pair of twisted pair.