How to write letter display system with single chip microcomputer?

Second, the hardware design and demonstration

According to the comparative analysis of the above system schemes, the overall system composition block diagram of this design is as shown in figure 1:

Figure 1 system overall composition block diagram

The whole system consists of three parts:

Module 1 takes single chip microcomputer 1# as the core, including 16*64LED lattice, driving circuit, STR4096 memory, wireless data transmission module, rotating chassis, photoelectric sensor, sound box and printer. Realization function: it is mainly used to realize the display of dot matrix, including the display of specific advertising language library content, timed time display, timed temperature display, and realize the display of various modes such as scrolling up and down, left and right; The memory is used to store the Chinese character lattice library and ASCII code, so as to realize the function of power failure without loss; The wireless module updates the slogan library and receives the setting information; The chassis can realize the left-right rotation of the display screen with adjustable swing amplitude; In the shopping guide of shopping malls, photoelectric sensors are used to detect people's entry and exit, which can be used in conjunction with automatic doors, and speakers play voice information such as "welcome"; In billboard applications, printers are used to print business cards.

Module 2 takes 2# single chip microcomputer as the core, including 4*4 keyboard, LCD and wireless data transmission module. Realization function: this part realizes the function of remote control, which can remotely set the scrolling mode of the display screen, select the advertising language library, set the time and set the swing range; Realize the update of advertising language library. (Please refer to Appendix 1 for instructions on using the keyboard.)

The third module takes the upper computer as the core, including the upper computer software and MAX232. Realization function: the upper computer mainly realizes the data update of the slogan library. The upper computer software sends the updated content (Chinese character built-in code or ASCII code) to MCU 2# through MAX232, and then wirelessly transmits it to MCU 1# to update the data.

The following is the specific design of each unit circuit:

1, master microcontroller

The main controller adopts 16-bit single chip microcomputer SPCE06 1A of Lingyang company. Because SPCE06 1A is built with 2K SRAM and 32K FLASH memory, it can meet the data processing and LED dot matrix display data storage requirements in this system. The CPU clock frequency is as high as 49. 152MHz, which can meet the refresh speed requirements. In addition, "6 1 board" also has the advantages of strong function, high cost performance, small size, high integration, easy expansion and low power consumption. , which simplifies the hardware circuit design of the main control system and has high reliability. Moreover, Sunplus MCU has an assembly language with C language style and a C language compatible with standard C. The functions of C language can be called by assembly functions, which makes the development and implementation of the whole system easier.

2.LED display drive circuit

In this design, the manufacture of 16 rows *64 columns LED electronic display screen and the design and manufacture of its display driving circuit are very key parts. The following mainly introduces the design of display drive circuit.

This LED dot matrix screen is displayed in a dynamic scanning mode, that is, scanning line by line. When working, first, a row of dot matrix fonts is output through column driving, then the decoder selects the corresponding row to display, then sends the next row of data, and then selects the next row to be valid until all 16 rows are scanned. At this point, a complete text message will appear. Then scan 16 lines repeatedly until new information is displayed. This method has the advantages of low power consumption, low cost and long service life, but it also has the problems of unstable display brightness and content display. According to the principle of visual retention, the complete display time of each screen should be controlled within 20ms, that is, 50Hz, so that people will not feel flickering at first sight. Because the dot matrix of 16 rows is to be scanned, the time of each row should not exceed 20ms ÷16 =1.25ms. The shorter the scanning time of each row, the better, because the brightness of LED is related to the current and the holding time. The single-point static current of LED lattice block is generally around 10mA, and the maximum single-point dynamic current can reach 160mA due to the duty ratio of116. In the case of constant holding time, the larger the current (not exceeding the rated current), the brighter the dot matrix brightness, while in the case of constant current, it takes a period of holding time to keep the brightness. Experiments show that when the current input of LED is 15mA, the maintenance time needs at least 1ms, otherwise the LED will be slightly bright. Because the clock frequency of SPCE06 1A single chip microcomputer is set to 24MHz in design, and there is 64-bit moving font data at a time, the calculated transmission time is less than 1ms, so that the latching function of column driver 74HC595 can be fully utilized, that is, the contents of this line can be displayed while receiving the next line of data to be displayed without latching new data, so there is no need for additional delay to increase the brightness of the display screen. By adopting this method, there is no need to increase the column driving devices of LED, thus simplifying the whole hardware structure and reducing the cost.

The processing of line signal is completed by 46 decoder CD45 14, and the output is high. Because the composition of the display screen line is composed of multiple modules in parallel, the power requirement of the line driver is relatively high, and we need to choose low behavior when scanning the line, so we add an inverter driver ULN2803 to meet the requirements.

The processing of column signals is mainly completed by eight 8-bit serial input parallel output shift registers 74HC595 with latches. The 64-bit dot matrix data serially output by IO port of single chip microcomputer is moved to the corresponding position bit by bit under the action of shift clock. After receiving the latch signal, the data is output to the column line of LED in parallel, and finally a row of LED pixels is illuminated by the row driving signal.

The circuit diagram of the display scanning circuit is shown in Figure 2.

Fig. 2 scanning driving circuit of LED display screen

3. Data storage

The design topic requirements can be added to 10 group of pre-stored information, and the display information has power-off protection function. At the same time, it is considered to load the Chinese character dot matrix font file HZK 16(26 1K bytes) and the ASCII code dot matrix font file ASC 16(4K bytes) into ROM memory, so as to find the corresponding font according to the built-in codes. Because the memory Flash of SPCE06 1 single chip microcomputer is only 32K, and it is necessary to store programs, so it is necessary to expand the data memory. We chose the supporting module SPR4096 of Lingyang "6 1 Board". SPR4096 is a high-performance 4m-bit (512kbyte) flash memory, which is divided into 256 sectors, each with 2kbytes. The working frequency of SPR4096 serial interface can reach 5MHz, and the data access speed and storage capacity can meet our requirements. The hardware connection diagram is shown in Figure 3: