PIC Microcontroller control of dot-matrix LED display technology research

        [Abstract] LED display technology in the industrial application of a wide range of instrumentation that can visually display the operating system, real-time status. At the same time as PIC microcontrollers feature strong advantages of low-cost applications in a variety of instruments in a wide range. PIC Microcontroller control of the dot matrix LED display technology research.
        [Keywords:] PIC microcontroller LED Control
        1, dot-matrix LED structure
        Use of LED for the 14 * 15 lattice, from 6 7 * 5 dot matrix LED plank, in the first three were used to form horizontal LED dot matrix 2 7 * 15, and then 2 7 * 15 ordered from top to bottom to form a required 14 * 15 lattice. When a line drive an LED where the lower column driven high, this LED is lit.
        Second, the composition of a static display circuit
        74LS164 for the TTL-way 8-bit shift register, enabling the serial input, parallel output. Where A, B (No. 1,2 feet) for serial data input, two pins according to the law of logic and computing the input signal, a total of 1, and then when the input signal. CLK (No. 8 feet) to the clock input can be connected to the serial port of the synchronous clock output. The rising edge of each clock signal, when added to the CLK terminal, shift registers shift one, eight clock pulses after the 8-bit binary number in all the immigration 74LS164. In the eight pulses are given after the first one the first to enter the 74LS164 data reaches the highest place, again a pulse, the first pulse will be out from the maximum displacement. 4 74LS164 phase series end to end, while the clock is then together ended.
        As long as we each chip LED on the 7 line in an input-driven low, this line in the corresponding column driver for high-point will be lit. So again to each row into the low, while the corresponding row is selected, the corresponding data into the column, and repeated scanning, because there is persistence of vision of the human eye can see the effects of the expected picture information .
        3, encoding
        Encoding method is determined by hardware design approach. Because the next row of three LED into the last one the last one drive is the first column of data into the 74LS164, so font encoding sequence and the order in the LED display just the opposite. And the PIC16F877 to do serial output when the SSPBUF register serial output 8-bit data in the highest bit is sent first, so each row is a right for the eight-point high low left encoded. Behind the analogy, to display a full 14 * 15 dot matrix requires a total of 28 groups of 8-bit two binary matrix data.
        4, PIC16F877 with the LED circuit connected
        PIC16F877 provides two serial communication module, namely the synchronous serial port and universal synchronous asynchronous receiver transmitter. Which MSSP module also provides two methods of work, one is a serial peripheral interface (SPI), another work by inter-chip communication bus (IIC). SSP module is mainly used for microcontroller and other peripheral interface or a serial communication between microprocessor chip, such as serial EEPROM, display controller, analog-digital converter and so on, all belong to the circuit board, a number of serial communication interface between devices. USART belongs to and the circuit board serial communication interface to external devices, simply put, is the RS232 interface, you can communicate with the PC. Therefore, we chose SPI synchronous serial communication lines into the election code. SPI works to provide 8-bit data transfer, SCK pin on the clock speed determines the data transmission speed. In the connected devices by the master device to generate the clock, other devices as external clock as the standard. Therefore, using the SPI mode, must determine that the device main controller parts, the other was from the controller parts. The circuit using the PIC16F877 as a master device, SSP module in master mode. SCK pin from the microcontroller to generate its own clock, so you can transfer data at any time, send in a write buffer SSPBUF when the action began, we use the SCK pin output serial output synchronous clock. This circuit is used to enter the SPI module out of the data, then the SDI pin can be turned off without, when SSBUF register where the contents of the clock according to a set by the SDO pin out. Set using the MSSP module's SPI work before the first thing is to initialize MSSP module, SSPCON register contains the relevant bits to be set up in the set is complete, home MSSP mode enable bit SSPEN, they can begin to SPI modeWork . At the same time, we must reset the SSP module, as long as the first SSPEN bit removed 0, and then re-set the SSPCON, then SSPEN can be set to 1. The equivalent of setting a good SSPCON set SDO, SCK, SDI, SS pin used for serial communication, so in addition SSPCON register settings, the right methods of work used in SPI pins must set up. SDO, and SCK as output pins, so TRISC

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