Design of Remote Data Transmission System Based on Single Chip Microcomputer Control System

1 Introduction

Most medium and large petrochemical enterprises in China use small current grounding system to supply power, and the power system is relatively large. Such systems generally have several or even more than a dozen 35kV general step-down stations and dozens of 6 10kv High-voltage Distribution rooms, which are widely distributed. Some substations are more than ten kilometers away from the general dispatching. Therefore, the accurate and reliable transmission of power parameters (voltage, current, phase, power factor, etc.) of each substation is particularly important for the timely decision-making of the general dispatching, improving the power supply quality and ensuring the safety of power operation. Here, we use a single-chip microcomputer to control the modem for remote real-time data transmission, and obtain satisfactory results.

2 hardware system design

The system network diagram is shown in Figure 1. The upper computer of the system adopts PII microcomputer, which is connected with the single chip microcomputer system as the lower computer through modem ←→ switching network ←→ modem. The data signal collected by the power sensor is input into the single chip microcomputer system. After being processed by the software program, the asynchronous transceiver 8251 controls the modem to dial automatically. After the upper computer responds, it sends out data. After the upper computer receives the data through the modem, it can carry out data table or graphic processing, which completes the whole process of remote data acquisition. The upper computer can perform patrol control and detection on multiple lower MCU systems through time-sharing modem.

The hardware circuit of single chip microcomputer system is shown in Figure 2. It is mainly composed of single chip microcomputer 89C51 and asynchronous / synchronous transceiver controller chip. Here, 8251 is used as asynchronous transceiver. Among them, com8046 is a programmable special clock generator, which can provide clock signal for 89C51 at the same time. The signals of receiving clock RXC and transmitting clock TXC required by 8251 are also provided by it.

Since the input and output of 8251 is TTL level, it is necessary to use serial transceiver driver for level conversion and driving. The system adopts commonly used mc1488 and mc1489 chips. RS-232 is a standard 9-pin interface, which can be connected with any standard external modem interface.

The performance requirements for modem are: telephone number parameter memory; It has automatic dialing function and automatic response function; Speed buffering and flow control; Mnp5 / v.42bis data compression mode is adopted; V4.2 error control protocol / MNP 2-4 error correction protocol is adopted; The speed is greater than 14.4kbps; Select standard products compatible with Hayes Series in the United States.

As the telephone line as the medium of the switching network will inevitably have line interference, the modem as the two ends must adopt corresponding anti-interference and error control technology. At the same time, the line transmission rate should not be too high. The baud rate of 1200dps is adopted in the system.

3 software design

The software design of single chip microcomputer system is mainly composed of 8251 initialization and data transmission. The program flow chart is shown in Figure 3 and Figure 4 respectively.

8251 initialization is set to: work in asynchronous mode; Baud rate is 1200dps; The data length is 8 bits, one stop bit; Even check is adopted; DTR and RTS signals are valid.

The control of the modem is determined by the DSR. When the DSR is valid, reset the modem first, and then send instructions to make the modem dial automatically. When the DSR signal remains valid, carry out data transmission with the upper computer.

In the data transmission program, a group of storage units store the data to be transmitted (i.e. the data input and converted by the sensor, or the manual input data extended by the keyboard system), and send the checksum data at the same time. After sending data, check whether the sending register is zero. If it is zero, it indicates that the data has been sent. After each data is sent, wait for the upper computer to return the signal. If it is incorrect, it needs to be retransmitted; If correct, continue to send the next data until the data is sent out.

4 Conclusion

Using single chip microcomputer to control modem for remote data transmission has achieved good results, and solved the problem of remote data exchange that can not be reached by LAN special line. It is especially suitable for remote areas, such as the patrol inspection of terminals, warehouses and high towers in remote places of enterprises.

The system can be extended on the basis of this hardware principle, which can increase the functions of display, key input, output control and alarm of single chip microcomputer, and realize the functions of remote key input data and parameter setting through key function conversion, so as to meet some special needs.

If different sensing methods are changed, it can be widely used in industry, agriculture and other occasions in society. Therefore, the system has a broad market prospect.

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