Design of human-machine interface module based on LPC2134

　　introduction

　　With the development of the power system, its system capacity is getting larger and larger, and its structure is becoming more and more complex. The information that the automatic control and relay protection devices in the system need to process is constantly increasing, which puts forward higher requirements for the functions of the human-machine interface. . The new human-machine interface module must be able to respond quickly and process large amounts of data, and have real-time information display and humanized interface functions. The rapid development of integrated circuit technology and embedded system technology and their application in power systems provide technical support for the upgrade of human-machine interfaces. This paper uses the research and development of fault line selection devices for small current grounding systems as the background, and uses high-performance and low-power integrated circuit chips to design a human-machine interface module based on ARM7. This module has larger capabilities than traditional human-machine interfaces. The advantages.

　　1 System structure

　　The functional block diagram of the human-machine interface module of this system is shown in Figure 1.

　　1.1 CPU system

　　The CPU in this module uses 32-bit high-performance and low-power microcontroller chip LPC2134. This chip has rich built-in hardware resources, including 32 KB of static RAM, 128 KB of Flash, 2 16C550 industrial standard UARTs, and 2 high-speed I2C interface and real-time clock, etc. This CPU uses three-stage pipeline technology, and instruction fetching, decoding and instruction execution can be completed at the same time. Its maximum operating frequency can reach 60MHz. The Vectored Interrupt Controller (VIC) can manage all 32 interrupt inputs, and the interrupt priority is programmable and dynamically assigned. The integration of these functions makes LPC2134 very suitable for industrial measurement and control, and is capable of controlling human-machine interface modules. Its CPU external reset chip can use CAT1025 produced by CATALYST Company. The CAT1025 combines non-volatile memory and reset functions. The memory uses a high-speed I2C bus interface (400 kb/s), which can support manual button reset input and write-protect input.

　　1.2 LCD interface

　　The liquid crystal module (LCM) uses SMG240128A dot matrix graphic LCD with built-in T6963C controller. This LCD has a single-screen structure, uses a single power supply, has 240×128 pixels, black characters/blue background, and is a medium-scale LCM. The interface circuit principle of the LCD module and CPU is shown in Figure 2.

　　In the LCD interface circuit shown in Figure 2, the control line of the CPU is first connected to the six-input inverter 74HC14 as the driver; the data line is connected to the bidirectional eight-bit bus transceiver 74LS245 as the driver. The chip has 2 control lines that can be controlled separately. Data transfer direction (DIR) and chip select (G). Compared with chip driving and resistor driving, the entire module structure is more compact and the circuits are clear, which can improve the system's integration and anti-interference capabilities. Potentiometer W1 is used to adjust the contrast of the liquid crystal, and W2 is used to adjust the backlight intensity of the liquid crystal. The user can adjust the display effect of the liquid crystal at any time as needed.

　　1.3 Keyboard and LED interface

　　The keyboard is mainly responsible for inputting user instructions, and the LED is responsible for indicating the system operating status. Traditional keyboards and LEDs often monopolize CPU pin resources. It can be controlled by I/O port level triggering. Although the matrix keyboard can save some pins, as the number of keys increases, the number of pins occupied will also increase.

　　In response to this contradiction, Zhou Ligong Company launched a button and LED driver chip ZLG7290. This chip uses an I2C serial interface and can provide a keyboard interrupt signal to facilitate the interface with the CPU. At least it only requires 2 I2C port signal lines. , so it can greatly save I/O resources; it can directly drive 8-bit common cathode digital tubes (less than 1 inch) or 64 independent LEDs; it can manage up to 64 buttons at the same time and automatically eliminate jitter, 8 of which Can only be used as a function key. Its biggest advantage is that the number of buttons and LEDs can be selected according to system requirements, and the expansion of buttons and LEDs does not require an increase in CPU hardware overhead. At the same time, it can automatically complete dynamic scanning of the keyboard and LEDs, saving CPU workload and concentrating resources. Used for signal detection and control. As an industrial-grade chip, this chip has strong anti-interference ability. It is widely used in industrial measurement and control. This human-machine interface module design uses 8 buttons and 8 LEDs, and the schematic diagram of the connection circuit is shown in Figure 3.

　　In Figure 3, ZLG7290 only needs to occupy three I/O lines of the CPU, which are the I2C port data transmission line SDA, the clock transmission line SCL and the key interrupt input INT. The I2C port of ZLG7290 is connected to the I2C1 port of LPC2134, and its transmission rate can reach 32 kbit/s. Since it is an open-drain port, a 1 kΩ pull-up resistor is required; the interrupt signal line can be connected to the external interrupt 3 (EINT3) of LPC2134 ) is connected to the input pin, and when a button is pressed, a button interrupt will be triggered. Of course, the signal line can also be left unconnected and the key detection can be completed by software query. R1~R8 are keyboard resistors, which can prevent the Dig signal line and Seg signal line from forming a short circuit when the button is pressed and affect the LED display; R9~R16 are current-limiting resistors with a resistance value of 220Ω. By appropriately reducing the resistance value, the value can be increased. LED brightness.

　　2 Software design

　　The software design aims to make full use of the system hardware resources to realize the functions required by the human-machine interface part of the small current grounding device. Specific functions include:

　　(1) The serial port receives and processes the normal information data and fault information data transmitted from the lower computer DSP;

　　(2) Real-time display of normal operation information of each line of the substation, including three-phase voltages Ua, Ub, Uc on the bus; three-line voltages Uab, Ubc, Uca; PT opening voltage (i.e. zero sequence voltage) 3U0; zero voltage of each outlet line Sequence current 3I0,

　　(4) When receiving fault information, interrupt the display of normal information, switch to the fault screen, and start the audible and visual alarm;

　　(5) Store ground fault information and file it as a fault record;

　　(6) Query normal operation information and ground fault information at any time; and set and modify system operating parameters according to authority;

　　To this end, a structured programming method can be used, from top to bottom, to gradually refine the problem solving process and proceed in stages, so that the problems handled at each stage are controlled within the range that people can easily understand and handle. The program hierarchical design scheme for the human-machine interface module of the small current grounding system is shown in Figure 4.

　　3 Human-computer interaction interface

　　This LCD can be controlled by its built-in controller T6963C. The instruction set inside T6963C is used to set the display function of the liquid crystal module, including setting the address pointer, display area, display mode, and data reading and writing mode. Graphic mode can be used to complete the display function. The display principle in graphic mode is to write the font data into the graphic display area byte by byte, and each bit corresponds to a pixel on the LCD screen. The contents of the system main menu and normal information display part are shown in Figure 5.

　　In Figure 5(b), 1#PT represents the 1# bus. The number of bus bars displayed can be set by on-site operating conditions. The upper right corner is the communication normal sign, and the lower right corner is the page turning sign. The fault information and history record query screen is shown in Figure 6.

　　Ground fault information usually includes the bus number, line number, fault phase, post-fault 3U0 value, ground fault occurrence time and disappearance time.

　　This design requires buttons to modify and store system parameters. The button panel is shown in Figure 7.

　　In Figure 7, a total of 8 buttons are set, including the four direction keys up, down, left, and right, the enter key, the escape key, the accumulation key, and the decrement key. The direction keys are used for silver submenus and display screens. Different setting bits can be selected when setting system parameters. The accumulation key and decrement key are used to modify parameter values ​​by adding or subtracting one; the enter key is used to enter the next step. First-level submenu and save modified data. The exit key is used to return to the upper-level menu. The functions of buttons and LEDs are implemented by the ZLG7290 chip with I2C interface by reading and writing built-in registers.

　　4 Conclusion

　　Through debugging and experiments, the human-machine interface module designed in this design can well complete the human-computer interaction function of the small current grounding device. This module uses a high-performance integrated circuit driver chip in the hardware, making the circuit compact and anti-interference strong. The functions of the software are also relatively complete, flexible, and easy to expand and upgrade. Based on the above characteristics, this human-machine interface module has good practical and promotion value, and can provide a certain reference for the design of human-machine interface modules in embedded system devices.