The man-machine interface is an important part of the embedded control system, which is used to exchange control systems and return system status in real time between human and machine. Most embedded systems use LCD screens and keyboards as input and output devices for human-machine interfaces. The human-machine interface designed here is an integral part of the data acquisition system, which provides convenience for system control and operation monitoring, and it has extensive practicability in various embedded control systems.
2 LCD display function realization
The liquid crystal display used here is RT320240B. The controller of this display uses the SED1335 controller manufactured by SEIKO EPSON. When the DSP accesses the SED1335, it is not necessary to judge whether it is idle. The SED1335 can be ready to accept the access of the DSP and correctly transmit the instructions and data sent by the DSP according to the internal timing. Considering that the RT320240B is a large-screen liquid crystal display, the display data acquisition waveform needs a faster screen refresh speed. Here, the parallel data transmission method is adopted, thereby improving the refresh rate of the liquid crystal screen in hardware design.
2.1 SED1335 controller
The SED1335 liquid crystal display controller consists of an oscillator, a function logic circuit, a display RAM, a management circuit character library and its management circuit, and a timing generator that generates drive timing. The oscillator operating frequency is selectable from 1 to 10 MHz. The display RAM of the SED1335 has the following features:
(1) Text display characteristic display RAM area is dedicated to text mode display, the data of each byte of the display RAM area is considered to be a character code, SED1335 will use the character code to determine the character first address in the character library, and then the corresponding font data Transfer to the LCD module. The 8&TImes of the character appears on the LCD screen; the 8 dot matrix is â€‹â€‹a byte of the text display RAM corresponding to 8&TImes; 8 dot matrix on the display.
(2) The graphic display characteristic display RAM area is dedicated to the graphic mode display, and the data of each byte of the display RAM area is directly sent to the liquid crystal display module, and the level state of each bit determines the display state of a dot on the display screen. , 1 is the display, 0 is not displayed. So one byte of the graphic display RAM corresponds to 8&TImes;1 dot matrix on the display.
(3) Character generator SED1335 manages the memory character generator CGROM. The character generator cures 160 kinds of 5&TImes; 7 dot matrix characters SED1335. Since SED1335 can only process 8-bit character codes, it can only display and establish up to 256 at a time. The characters are given in the character table of SED1335, and the contents of the internal character generator are given. At the same time, the character code ranges 80H~9FH and E0H~FFH of the extended character generator are given, a total of 64 kinds.
2.2 LCD display hardware circuit design
Considering the characteristics of the SED1335 controller and the speed requirements of the display waveform, a parallel data bus approach is applied. The DSP2812's external data bus just meets the need to transmit data in parallel. I/O data buffer interface A0 selects the lowest address bus A0 of the external address bus, writes the instruction code to the external address of "*******1" through XINTF, and writes the data to "* The external address of ******1" is so clever and convenient to solve the setting of A0 port, and it is convenient for programming. Based on the above considerations, the hardware connection circuit of the liquid crystal panel is as shown in FIG.
2.3 LCD display software design
The LCD display function is implemented by writing to a specified memory area. The contents of the display buffer area are read by the read command, and compared with the write data, the display buffer area RAM function can be effectively detected, and the liquid crystal display is comprehensively detected by combining the instructions provided by various SED1335 controllers.
In combination with the characteristics of the DSP itself, the system hardware circuit must first define the data segment LCDCMD, LCDDATA when writing the software program, and explain in the main program:
#pragma DATA_SECTION(LCDCMD, "LCD_CMDFile")
#pragma DATA_SECTION(LCDDATA, "LCD_DATAFile")
Then assign addresses to the two data segments in the CMD:
LCD DATA: origin=0x0080000, length=0x00001
LCD CMD: origin=0x0080001, length=0x00001
Figure 2 shows the design flow of the LCD display software.
The common serial port LCD screen speed of the same size is generally 2~3 s. Using the parallel port expansion data bus design method can increase the brushing speed to 0.5 s, which meets the design requirements. If the design is developed in assembly language, the screen speed will be Faster.
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