Intelligent Broadcasting System Control Based on P89C51RA

1. Introduction

With the development of computer technology and multimedia technology, computers are increasingly being used in all areas of society. Intelligent broadcasting system is a comprehensive application of computer technology and multimedia technology in broadcasting system. It is to add computer system and controller to the original broadcasting system to realize the intelligent upgrade of broadcasting system. Intelligent broadcasting system has the following functions: programmed automatic broadcasting; broadcasting zone preset; unattended full automatic operation; support for multiple broadcasting modes. On the one hand, intelligent broadcasting system can greatly reduce the workload of radio program production and broadcasting personnel, and on the other hand, it also provides rich materials and program sources for the production of radio programs. Intelligent broadcasting system will be widely used in large, medium and small schools and some enterprises and institutions.

The intelligent broadcasting system is mainly composed of computer software system, computer hardware system, controller and original broadcasting system. The controller plays the role of a bridge connecting the computer system and the original broadcasting system in the whole system, and realizes the interpretation and execution of various control instructions issued by the computer. Therefore, the performance of the intelligent broadcasting system controller determines the safe, reliable and stable operation of the whole system to a certain extent. This paper studies and develops an intelligent broadcasting system controller based on P89C51RA to realize the safe and reliable operation of the whole system.

2. Composition of the intelligent broadcasting system controller

The intelligent broadcast system controller is required to accurately receive the control commands and control information sent by the PC host, and safely and reliably control the corresponding broadcast equipment and broadcast partitions. Therefore, in the system design, we strive to achieve the control of the intelligent broadcast system with simple hardware circuits and the simplest and most effective control algorithm. Since the PC host, controller and broadcast equipment are all located in the same room and are close to each other, RS-232 serial communication is used between the PC host and the controller, and relays are used to control the on/off of the broadcast equipment and broadcast partitions. The system structure block diagram is shown in Figure 1.

Working principle of the system: First, the PC host sends corresponding control instructions and control information according to the current time, requiring the controller to turn on the corresponding broadcasting equipment and connect the partition switch that currently needs to receive the broadcast program; then, the controller analyzes the received information to determine the correctness of the received information, and sends confirmation information or receives error information to the PC host. If the received information is wrong, no action is performed, otherwise the corresponding broadcasting equipment is turned on and the required broadcast partition is connected as required; after completing the above operations, the controller continues to wait for commands from the PC host.

3. System hardware circuit design

3.1 Single-Chip Microcomputer System

At present, the development of single-chip microcomputers has far exceeded the meaning of the name "single-chip microcomputer". Most companies have launched enhanced single-chip microcomputers that integrate rich resources and adopt many latest technologies. In system development, how to choose a single-chip microcomputer with excellent performance and low price will greatly improve the performance of the system we design while reducing the cost.

The system uses the enhanced 8051 microcontroller P89C51RA launched by Philips. Philips is the first company to obtain the MCS-51 technology license. It has made outstanding contributions to the inheritance and development of the MCS-51 series of microcontrollers using new technologies and has achieved many breakthroughs. For example, based on the standard RS-232 interface, the in-system programming (ISP-In System Programming) function of the microcontroller with internal integrated Flash memory can be realized through simple external switch control. So far, Philips has launched more than hundreds of 8-bit, 16-bit and 32-bit microcontrollers. Therefore, Philips provides us with good conditions for choosing the most cost-effective and highly stable microcontroller according to different system needs. The P89C51RA microcontroller used in this system is a high-cost-effective, highly integrated microcontroller with integrated Flash memory and ISP function. The P89C51RA microcontroller integrates 8k Flsah program memory, 512 bytes of data memory (RAM), and dual DPTR, which lays a solid foundation for the system's circuit simplification and program design flexibility.

3.2 Serial Communication Interface Circuit Design

The PC is equipped with a standard RS-232 serial interface, while the input and output of the microcontroller are both TTL levels. The electrical specifications of the two are different. To achieve data communication between the microcontroller and the PC, the TTL level of the microcontroller output must be converted. Here, the high-performance RS-232 transceiver chip SP232E launched by Sipex is used. It fully meets the RS-232 and V.28 serial protocols, has enhanced ESD performance and a data transmission rate of 120Kbps. This chip is fully compatible with MAX232, but after comparison, it is found that its stability and anti-interference ability are better than MAX232. The schematic diagram of the serial communication circuit of the system is shown in Figure 2.

3.3 ISP Circuit Design

The ISP function of P89C51RA is completed through the standard RS-232C serial port. It is an embedded online programmable function. To realize the ISP function, only a small amount of circuit board area and components need to be added. Therefore, as long as the single-chip system is equipped with an RS-232 interface, the program can be downloaded directly through the serial communication cable, which is very convenient to use. The design of the single-chip system with ISP function is no different from that of the ordinary single-chip system in other aspects. It only needs to add the ISP hardware activation switch to the design of the RS-232C serial port. For P89C51RA, the programming voltage VPP = 5V, so the circuit principle of the ISP hardware activation switch is shown in Figure 3.

Implementation of ISP function: When the double-pole double-throw switch S2 is downward, the PSEN pin of P89C51RA is grounded, the ALE pin is suspended, and the EA/VPP pin is connected to the 5V programming voltage. At this time, press the reset button S1, and the microcontroller enters the ISP state after reset. At this time, the Flash program memory of the microcontroller can be erased and written in the FlashMagic software or ZLGISP software environment. When the double-pole double-throw switch S2 is upward, the microcontroller enters the normal working state after power-on or pressing the reset button S1. For details on the implementation of the ISP function, please refer to relevant information.

ISP is an excellent function of P89C51RA MCU. It not only greatly facilitates the debugging and writing of MCU programs in system development, but also enables the system to have online upgrade function.

3.3 Design of broadcasting equipment and broadcasting zone control circuit

Broadcasting equipment and broadcasting zone control are both implemented using relays. In order to ensure the long-term safe and reliable operation of the system, the system uses OMRON G2R-1 DC12 relays with a single-point contact current of 10A. The rated control voltage of the relay electromagnetic coil is 12V DC voltage and the rated current is less than 50mA.

The system uses the high voltage and high current eight Darlington transistor array integrated circuit ULN2803, and the maximum driving voltage/current of each Darlington transistor is 50V/500mA. The design of ULN2803 is compatible with the standard TTL level, which makes the device widely used in computer control, industrial control and consumer products.

The selection of ULN2803 has greatly improved the reliability, stability and simplicity of the drive control circuit. The principle of the system drive control circuit is shown in Figure 4.

4. System software design and implementation

In order to improve the reliability of the system receiving information and the working efficiency of the CPU, the serial communication of the system software adopts the interrupt mode. Therefore, the system software mainly consists of two parts: the main program and the serial communication interrupt service subroutine. The main program flow chart is shown in Figure 5 below.

The working process of the serial communication interrupt service subroutine is: first turn off the system interrupt, then clear the receive interrupt flag, then complete data reception, and finally turn on the system interrupt. Turning off the system interrupt during data reception is a necessary condition to ensure reliable information reception, and must be given sufficient attention in software design.

5. Conclusion

The intelligent broadcast system controller based on P89C51RA in this article is just one example of the new MCU being widely used in various industries. It has been running stably and reliably in the intelligent broadcast system. This example can also be further expanded and applied to security, industrial control and other fields.

The author's innovation is to use Philips' P89C51RA microcontroller and Darlington transistor array ULN2803 to greatly simplify the system hardware structure, and use the ISP function to give the system online debugging and upgrading functions.