Resolution of serial port protocols

When we learn the principles of the microcomputer, many people will have a big problem with some interface bus. These are some of the content contained in the serial port protocol. So in order to better understand some interface serial port protocol standards, we will give a detailed introduction to such problems.

Serial Port protocol plug-in type and conversion

The serial port protocol is an interface standard, which specifies the electrical standard of the interface, simply put, it is only a standard of the physical layer. It does not specify the interface plug-in cable and the protocol used, therefore, as long as the interface plug-in cable we use conforms to the serial port standards, it can be used flexibly in practice. In the serial port interface standards, various protocols are used for communication and Device Control ｡

We have learned about the serial port protocol. In our daily work, we are most exposed to the external interfaces of some actual devices. How can we know from the shape that this interface is? How do I define each pin of a cable? Above we know the serial RS-232, RS-422 and RS-485 standards only to interface electrical characteristics to make provisions, and does not involve connectors, cables or protocols, on this basis, users can establish their own high-level communication protocols. The most frequently used plug-ins we encounter in our actual work have three DB9 DB25 RJ45 plug-ins. The above three plug-ins can be used as serial port plug-ins, you can also switch between sockets through cables. Next we will describe the pin definitions of the three sockets separately. The conversion between the three sockets can also be achieved by jumping the cables defined by the sockets ｡

Another type of plug-in port is RJ45. For example, The SNI high mss1600 and mss700 video servers used by Hubei TV station all have serial ports, the plug-in ports are RJ45, and the serial port plug-in of the broadcasting controller is DB9, therefore, we need to use a conversion cable ｡

RS485 half duplex method: RX + and TX + are connected to Data +; RX-and TX-are connected to Data-. RS485 FULL duplex/RS422 method: FULL And GND transient; the signal line is RX +, TX +, RX-, TX-. You can connect to GND as needed ｡

Serial Port protocol Extension

We know that a computer usually has two serial ports. For a broadcasting control computer, there are far more than two devices to be controlled. We need to control the video server at the same time, video Recorder, switching Platform, and screen reader. Therefore, we need to expand the serial port. We can use the serial port expansion card to expand the serial port, for example, we use the serial port expansion card MOXA CI-134 in the broadcasting control system ｡

MOXA CI-134 is a RS-422/485 4 serial port card designed for Industrial communication applications. It supports 4 independent RS-422/485 serial ports in One-to-multiple point communication applications, up to 128 devices can be controlled. To make RS-485 2-wire half duplex operations easier, each CI-134 card has automatic data flow control (ADDC) without software operation. Therefore, in Windows applications, RS-485 half duplex protocol can be controlled without additional coding. To meet industrial requirements for high reliability products, this series of products provide optional photoelectric isolation (2 KV) and Surge Protection (25 kv esd) functions ｡

This product features: Optional photoelectric isolation (2KV) and Surge Protection (25KV ESD) features; Automatic Control of Data flow ADDC (Automatic Data Direction Control) features; RS-485 Data Control l: ADDC can be controlled through the RTS; built-in terminal resistance; chip hardware traffic control to ensure no data loss; advanced ASIC design, low rework rate; support for many common operating systems ｡

Application of serial port protocol in broadcast Control System

We know that the serial port RS232 valid transmission distance is 15 meters, the maximum transmission distance of the RS-422 is 4000 feet (about 1219 meters ), the maximum transmission rate is 10 Mbps. The video recorder used in broadcasting control, such as DVCPRO and IMX, has RS232 and RS422 interfaces. If pin9 is used, RS422 is used, the Video Server codec port control is the RS422 interface, but the plug port is RJ45, not DB9, and the switch cable is needed for conversion. Therefore, we can flexibly use the above features in the control, the RS422 switch is selected for switching between the master and slave nodes and the distance. The RS232 control interface is used for controlling the RS422 switch, this switch is directly controlled by the COM port of the broadcasting controller itself for switching. Other control recorders, switches, and video server encoding/decoding cards use the RS422 interface extended by the MOXA card to switch to the RS422 switch for switching ｡

In the whole system, only the RS422 switch opening control is the COM (RS232) Port Control of the broadcasting control machine. Others are the RS422 interfaces extended by the MOXA card, an RS422 to RS232 converter is added in front of the emergency switch because the emergency switch requires RS232. Broadcast control commands can be issued through the control line broadcasting control machine in a timely manner, you can also read video recorders, switch servers, and video servers at any time ｡

The RS422 bus, RS485, and RS422 have the same principle. They are sent and accepted in a differential mode, and do not require a digital ground. differential operation is the root cause of long transmission distance at the same rate, this is the fundamental difference between the two and RS232, because RS232 is a single-ended input and output. During duplex operation, at least three lines (asynchronous transmission) are required: The digital ground, the transmission line, and the receiving line ), you can also add other control lines to complete synchronization and other functions. RS422 can work in full duplex mode through two pairs of twisted pair wires without affecting each other, while RS485 can work in half duplex mode only, and the sending and receiving cannot be performed at the same time, however, it only requires a pair of twisted pair wires. The above three interfaces have their own shortcomings and can be flexibly selected as needed in actual work ｡

Computer control is increasingly widely used in broadcasting and broadcasting control systems. With the continuous development of computer technology, intelligence will also increase, and the system will become larger, this requires us to have a better understanding of the basic theory of computer, so that we can have a better understanding of the system, maintain the system, ensure the safe and stable operation of the system, and better ensure the security of broadcast ｡