Application of serial port server in broadcast monitoring

1. System Principle

RS-232 interface Also called a serial port, asynchronous port or a COM port, it is an interface between DTE (data terminal equipment) and DCE (data communication equipment). DTE includes computers, terminals, serial printers and other devices. RS-232 is defined as a single-ended standard that increases the communication distance in low-speed serial communication. RS-232 adopts an unbalanced transmission method, which is the so-called single-ended communication. The RS-232 serial port uses a level method for data transmission, and the transmission distance is generally short, so RS-232 is only suitable for communication between local devices.

Currently, the more commonly used serial ports are 9-pin serial ports (DB9) and 25-pin serial ports (DB25), which can be directly connected to standard RS-232 ports (RS-422 and RS-485 are farther away) with cables. The simplest and most commonly used is the three-wire connection method, that is, the grounding, receiving data and sending data are connected. This article only involves the most basic connection method, and directly connects with RS232.

DB9 Common Pin Description Serial port data transmission can be realized as long as there are receiving data pins and sending pins. For 9-pin serial ports and 25-pin serial ports, 2 and 3 are directly connected. The above table is for the standard serial port of microcomputers. For many non-standard devices, a principle is: the receiving data pin (or line) is connected to the sending data pin (or line), cross each other, and the signal ground is connected accordingly.

DB9 Common Pin Description

Since RS-232 has a short transmission distance, it cannot connect long-distance devices, and devices with serial port (RS-232) management functions cannot be managed and accessed through the Internet. At this time, we can use advanced TCP/IP technology and management methods to transform these devices. The serial port server is a communication interface converter that completes data conversion between RS-232/485/422 and TCP/IP, providing two-way transparent data transmission between RS-232/485/422 terminal serial port and TCP/IP network. It can connect multiple serial port devices and select and process serial port data streams, convert existing RS-232 interface data into IP port data, and then perform IP-based management and IP-based data access.

It integrates ARP, IP, ICMP, TCP, UDP, DHCP, SOCK5 and other protocols, supports gateway and proxy server, and the parameters can be set through the browser. It supports point-to-point and point-to-multipoint connections, and supports broadcast or multicast. Different serial ports can be configured into different modes to meet different application requirements.

The serial device server has the following three working modes:

Use virtual serial port communication mode (TCP realport): In this mode, one or more converters are connected to a computer to achieve two-way transparent data transmission. The virtual serial port software on the computer manages the converters below, and one virtual serial port can correspond to multiple converters, and N virtual serial ports correspond to M converters (N<=M). This mode is suitable for RS232 device connections controlled by computers.

Based on network communication mode (Tcp/Udp socket): In this mode, the application on the computer writes the communication program based on the SOCKET protocol, and directly selects the support of the SOCKET protocol in the converter settings. The serial port server completes the storage control of the communication data between a connection-oriented RS232 link and a connectionless Ethernet. The system processes various data, processes the serial port data stream from the serial port device, and converts the format to make it a data frame that can be transmitted in the Ethernet; judges the data frame from the Ethernet, and converts it into serial data to send to the serial port device that responds.

Point-to-point communication mode (PPP): In this mode, the converters are used in pairs, one as the server and the other as the client, and a connection is established between the two to achieve bidirectional transparent data transmission. This mode is suitable for transforming the bus connection between two serial devices into a TCP/IP network connection.

2. System Application

In the past, centralized monitoring systems for broadcast transmission and transmission generally used modems for data transmission. With the development of network technology and the popularization of the network in the broadcast industry, remote monitoring and remote data collection through LAN and Ethernet have become the most economical and reliable way. We can connect serial devices to the network without knowing the complex TCP/IP protocol and without changing the user program.

This article takes Kanghai NC600 serial port server as an example to discuss the design scheme of the centralized monitoring system of broadcast transmission room equipment and the data acquisition system covered by broadcast FM.

The system structure of centralized monitoring based on LAN and remote data acquisition over WAN using serial port server is as follows. The monitoring center is responsible for communicating with field equipment to receive various field equipment information and control field equipment, and at the same time remotely monitors and controls each frequency modulation coverage point equipment through Ethernet. The topology structure is as follows:

In the following practical application of serial port server, we take Kanghai NC600 as an example.

1. Network device detection

The supporting software of serial port servers such as "VSPM Virtual Serial Port" has advanced network detection function. No matter how many serial port server devices there are in the LAN, they can be scanned out within 1~2 seconds and displayed in detail to the user. It only takes two clicks of the mouse to map the remote device port to the local virtual serial port. The whole process does not require entering any serial port server data. The parameters of the virtual serial port are automatically synchronized with the serial port server. After the software is installed, users can find the serial port management software in the control panel of the XP operating system.

2. There are three ways to enter the serial port server for setting

First, log in through a WEB browser: directly enter the IP address of the serial port server.

Second, remote login via TELNET: If the serial port server and the PC used for monitoring are not in the same network segment, you can add a route to connect the PC and the serial port server.

Assumptions: NC600 IP address: 192.168.0.233 XP system IP address: 24.0.46.144 Run under DOS command: route add192.168.0.23324.0.46.144Third, use the serial terminal to manage the serial server locally through the CONSOLE port. Connect the terminal serial port to the CONSOLE port of NC600, the terminal baud rate is 9600, data bit 8, stop bit 1, no parity.

3. Setting of serial port server parameters

A. Set IP address: Change the original IP address of NC600 to the IP address you need in [Ethernet IP Address] and [Ethernet Subnet Mask]. If it is connected to the host through a router, enter the address of the router or gateway in the default gateway.

B. Serial port settings

C. Working mode setting: The detailed parameter settings have different parameter options for different working modes.

The application of RS232 in the transmission room is mainly used in the local area network, using the virtual serial port communication mode. Each PC needs to install the supporting software of the serial port server such as "VSPM Virtual Serial Port". Different applications correspond to different virtual serial ports. There are mainly three applications:

1. Application in audio signal switching: Connect the COM1 interface of the audio switching device to the serial port server through the serial port cable provided. The serial port server is connected to the local area network. Any PC in the network can install the corresponding software to operate the audio switching device.

2. Application in live satellite broadcasting: Our station uses ABR202 series satellite receivers. During satellite broadcasting, we modify and query signal parameters through serial port software such as HyperTerminal or CRT. Using a serial port server not only solves the problem that one PC can only connect to one satellite receiver and cannot be used as both the main machine and the backup machine, but also saves rack space and can designate any PC in the network to monitor the satellite broadcasting situation.

3. Application in network timing: A FORTUNE GPS clock is connected to the serial port server through the COM1 port. Any PC in the network can install the GPS timing software to perform network GPS timing on the PC.

Application of RS232 in remote monitoring: Based on the network communication mode. We mainly solve the parameter adjustment of satellite receivers, FM audio monitoring and FM transmitter power monitoring. In practical applications, we can connect the satellite receivers, audio monitoring and exciters or some environmental monitoring equipment in the remote FM room to the serial port server through the COM port, and then choose different network access methods according to our needs.

Taking the NC600 series serial device server as an example, it provides a V35 optional module with a standard V35 interface, supports a complete TCP/IP protocol stack, supports ARP, IP, ICMP, UDP, PPP, TELNET, FTP, PPPoE and other protocols, and supports ordinary modems, GPRS/CDMA modems and other network access methods.

1. Application in satellite signal reception: The satellite receiver is connected to the serial port server through the COM port. We can monitor the satellite signal reception, adjust the reception parameters as needed, and select different audio for downloading.

2. Application in FM transmitter: Audio monitoring equipment and FM exciter are connected to the serial port server through their respective COM ports. We can monitor the transmitter's transmission status at any time, monitor the listening effect, and then adjust the power of the transmitter, turn it on and off as needed.

3. Application in environmental monitoring: Due to the particularity of broadcast transmission, in order to ensure the safety of equipment in the transmission room, we can also install some environmental monitoring equipment with COM ports, such as fire prevention, intrusion prevention, etc.

As for the software, we must first set the serial port server to work in TCPclient mode. The monitoring and control software passively waits for the serial port server to connect on the specified TCP port. When the serial port server is powered on, it actively requests the monitoring center to establish a TCP connection. Once the connection is established, it will remain unless the monitoring software actively requests to disconnect.

This ensures that the data channel between the monitoring software and the serial port server always exists. After the TCP connection is established, if no data communication is performed, it will not occupy any network resources. Since the TCP connection always exists, even if two or more field devices send data to the monitoring center at the same time, it will not cause any problems. Because each TCP connection is managed by a different Win Socket, when a TCP connection receives data, the corresponding Win Socket will notify the corresponding software to process the data through the receiving data event. The monitoring platform can send data to the field device at any time without having to pay attention to the communication status of other field devices and the platform software.

3. Conclusion

With the new development of broadcasting, "connecting all devices to the network" has become a consensus in the development of broadcasting technology. In order to solve the decentralized and centralized monitoring problems of broadcasting equipment, keep up with the trend of network automation, and establish competitive advantages, we broadcasting technicians must establish a centralized network monitoring system for high-quality audio acquisition, transmission and emission. The serial port server is like a microcomputer with a CPU, real-time operating system and TCP/IP protocol, which facilitates data transmission between serial ports and network devices. It allows us to access, manage and configure remote device serial port servers through the network with a PC at any location in the radio and television network, and uniformly manage and monitor the serial port devices connected to the server.

The application of serial device servers can provide a complete remote management solution for the transmission and emission monitoring of broadcast signals. The traditional decentralized maintenance and monitoring methods waste manpower and material resources and have poor reliability. The application of serial device servers on the basis of existing networks is fundamentally aimed at improving the quality of maintenance management, improving overall work efficiency, protecting safe broadcasting, and providing technical support for the healthy development of broadcasting.