LED dot matrix display is a collection of electronic micro-electronics technology, computer technology, information processing technology in one large display systems. It has its colorful, wide dynamic range, high-brightness, long life, stable and reliable work of the advantages and become a media show, as well as outdoor display ideal for operations. At the same time can also be applied to a wide range of military, railway stations, hotels, sports, news, finance, securities, advertising, as well as transportation and other industries.

At present, most of the LED dot matrix display systems bring their own character. Dynamic display and its effects (mainly the content of the show rolling) mainly depend on the realization of the scanning hardware drivers, the method is relatively easy, but can only show in advance in accordance with the design. In fact often encounter the special requirements of the dynamic display, such as elevators running up and down in the direction of the arrow move, some of the smart meter amplitude of the strip shows, advertising display manufacturers, such as trademarks. At this time of the general display system will be very difficult to meet the requirement. In addition, due to the limitations of memory itself, its special character or symbol is often difficult to show that the content of the show at the same time can not tamper with them. In this paper, the use of a PC and single-chip control of the LED display system of communication. This method can display the content (including Chinese characters and special icons) in real-time control, so as to achieve, such as flashing, scrolling, typing and other dynamic display. The method also can adjust the dynamic display of speed and at the same time PC users can also drive on the preview display to show real-time content can be modified. In addition, the adoption of the standard RS232/485? Conversion module can also display system for the remote control.

2 hardware design

The system's main hardware design is the next-bit single-chip machine's display? Part of the control. The host computer (PC machine) and single-chip display control part of the standard RS232 interface for communication. For remote control, we need only to increase to RS232/485 converter module, which has been part of the mature circuit design, it is no longer described in detail.

Specific LED display control circuit shown in Figure 1. Single-chip circuit as a whole by the 89C52, dot-matrix data memory 6264, driven out circuit ULN2803, line drive circuit TIP122, shift register 4094 and the subsidiary circuit. The circuit designed by e-screen display of 10 characters, need 40 8 × 8? LED dot matrix module can be composed of 16 × 160 rectangular lattice. As a result? AT89C52 only 8k of storage, and display the content from the PC control, it is not possible to advance the need to make dot-matrix display the contents of the existence of single-chip, but only by the PC real-time machine to show that the requirements of Dot-matrix data into the buffer zone and to the MCU 6264.

The circuit shows the use of progressive-scan mode. Work by the single chip removed from the buffer zone in the first line need to show that the 20-byte array of data, and then out by the dot-matrix data input according to the P1.2-mouth in turn out to enter the serial shift register, the data entry In the order and display the contents of the order of the contrary. And then buy-side line dot matrix strobe P1.3 1, that is, the home of the D line shift register for the high, STR enable (OE pin all of 4094 then +5 V level), making out in the shift register At the same time, parallel output data strobe to the bank. After a period of time delay before the next line dot matrix display data. It should be noted that each party can only strobe data, that is, through constantly to achieve the progressive-scan display Chinese characters or characters.

3 shows the design and control

The author in the design of PC control Display System in single-chip multi-use PC machine to achieve the main functions of the single-chip display sub-system, including the choice of display options (including static, flashing, scrolling, typing, etc.), rolling direction Choice (including rolling up and down and rolling around), dynamic display the speed of adjustment (that is, the frequency of flashing text, scrolling speed, typing speed display, etc.), display the contents of the import and preview show, and so on. Single-chip through the general RS232/485 serial PC to receive the Machines issued by the show refers to the use of timer interruption means scanning lines, each interrupted his show, interrupted from time to time to time 1.25ms, so the screen refresh rate for the whole? 50Hz, Thus no sense of blinking.

Dynamic display of speed adjustment method is usually to change the timer interrupt, but when the show is slow, easy ways to make the whole screen refresh rate lower, so that the content of the show emerged blinking. As a result, the design uses a "soft-time" method, that is, in the process of naming a variable as a "soft-timers" to be used to set up two dynamic display of the interval. In the time of the interruption call count, if the number of calls to reach settings, change the content of the show. In order to ensure the proper display, "soft timer" settings must be greater than the whole screen display cycle. As the screen shows every line of 1.25ms, full-screen display for the cycle of 20ms, taking into account the margin, can be soft-timer settings set at more than 30ms. This cycle count, you can achieve dynamic display. "Soft-timer" settings by PC PC machine to change, can achieve this? LED dynamic display of speed regulation, but also to maintain the flow and content of the show without a sense of flickering.

3.1 single-chip control of dynamic display

Static mentioned above, flashing, such as typing and scrolling display 4, is in fact single-chip interrupted regular procedures to deal with different line scanning method. The following will be how to achieve this display of 4.

Static display only interrupted from time to time in the process transferred from the buffer zone shows that the data show that his party, and then select the bank to achieve the bank's show, so the cycle can show the entire content. Flashing display Similarly, different intervals to a "soft-timers" from time to time, line scan, the shift register of the D-side into the All-0, making the whole screen does not show in order to ensure that Black screen time and show the same time, in order to achieve the Chinese characters or icons of the flashing display.

Rolling request show that the contents of every show needs some time to the designated direction (from right to left here as an example) a mobile, so that the display can show more. To this end, the need for the next show, before moving on display the contents of the buffer zone to make changes in order to complete the corresponding array of data transfer operations. To do:

Set up a buffer zone display (shown in Figure 2), the area should be composed of two parts: one for the preservation of the current LED display to show the 10 Chinese characters dot matrix data; another part of the dot-matrix data for the pre-loading zone for Save about to enter the LED display an array of characters of data. Rolling indicators point to always display the origin of the far right. When rolling pointer to the need to move the dot matrix display data storage area of the first characters of an address for the first time, LED display shows the buffer zone empty, and the pre-loading zone saved the first to be a dot-matrix display Chinese characters of data. When rolling show, we can scan in the next cycle of scanning every line break in the process, it will show the corresponding buffer line to the left of a dot-matrix data at the same time to change the display buffer. (It should be noted that, it is necessary to ensure that the operation in the interruption of 1.25ms time. Here? 89C52 use 22MHz crystal, the experiment proved that this operation can be achieved). In this way, in a cycle of scanning, the entire Chinese characters will be a left, and show the contents of the buffer zone at the same time to change. As the pre-loading zone to preserve the data on an array of Chinese characters, that is 16 × 16 dot matrix, the current display the contents of the buffer zone can only move 16. When the next arrival of the rolling, rolling pointer will be moved to a dot-matrix data storage area for the next character in the first address, and pre-loading zone into the Chinese characters dot-matrix data. Then repeat the above operation can achieve the show rolling. Special characters or graphics display Similarly, will not go into here.

Shows that require typing Chinese characters on the screen from left to right according to the order of one, like typing. Design options are as follows: First of all, LED display will show the corresponding buffer zone cleared of all, that is? LED display blank, and then every interval of a "soft-timer" set by the dynamic display of time, showing the buffer zone in order to join a Chinese character Dot-matrix display data and scanning, can achieve this type show.

3.2PC control procedures
A. The realization of communication

In the Windows environment, to achieve single-chip PC with the Windows communications can be used for communication API function or use of VC + + (or other language) standard communications function _inp, _outp to achieve. However, both methods cumbersome, and the use of ActiveX controls MSComm32 is very easy to achieve. Control of the incident by way of simplifying the operation of the serial programming and set up serial communication to send and receive data, but also for serial status serial communication and information formats and protocols set. Its initialization procedure as follows:

Under normal circumstances, PC with a number of 89C51 single-chip system master-slave communication, in order to distinguish between the single-chip system that can make use of 89C51 Serial mode 3, that is 11 asynchronous receiver / Send the way, the way The effective data for 9, 9 for the first address / data flag, its role is to make the machine from which to send the data to determine whether or not to address in order to achieve multi-machine operation. However, due to the MSCOMM control is achieved between the PC and single-chip communication, which is a standard 10-bit serial communication, that is, the standard 8-bit data and the data start-stop - An all. Therefore, the two formats are incompatible, it is difficult to use for this option. Therefore, consideration could be given to single-chip approach the work of a serial set, that is, an 10-bit asynchronous receiver / sending to resolve, and its communication processes are as follows:

First of all communications made mark the beginning and then send the needs of single-chip operating system address, and then send the work shows that the word order, the order includes 2 bytes, one byte for the pre-set display and rolling direction, after a byte Is set to show the speed. Another is sent down the contents of the dot matrix display data, a final check of the data. The Statute of the communication is very simple and be able to better address these problems in order to achieve single-chip PC and multi-plane between the master-slave communication and control of the show.

It should be noted that, when the need to change the content of the show, in order to avoid interruption in the single-chip serial data receiver, garbled screen, the screen should not show (in "black" state) until receiving the data completely , The serial interrupt handling at the end of another show.

Chinese extraction matrix is the key to this article from the data matrix UCDOS under the font file HZK16. In this regard, introduced more literature [2] gives more specific VC in the matrix of Chinese extraction under the program will not go into here. For special characters or graphics array of data extraction and simple way to do a BMP file, and then take some of the software module (such as the extraction matrix v2.1) to get. In order to facilitate the display, dot-matrix data format should be n × (16 × 8), less than should be required to add data to 0. b. Dynamic simulation results show.

In order to facilitate the adjustment of the LED display, in the author PC control machine interface designed simulate the LED screen display, with the actual show exactly the same effect. Users can set the display mode and display the speed of adjustment, and then show the effect of the interface for preview, and can be amended at any time and set parameters, which are very simple and convenient.

To this end, might start with a virtual interface depicting the LED display, as the actual display for the 160 × 16 dot matrix, the interface must be set the same region.

To achieve dynamic results show that the method and similar to the above, here on a rolling display as an example to make a note. The need for scrolling text, you can set it to bitmap format, in the temporary memory, and then use the VC provide bitmap copy BitBlt function will copy the bitmap to show the location. For special characters or graphics, you can directly use the BitBlt function call to the location of the show. Then in the category CLEDDlg the OnTimer function in the function call in order to achieve a rolling text of the show. In addition, can also set different response time to change the text of the scroll speed.