Various LED display systems make us dazzled, but the LED display control system hardware has many similarities, such as high-end products full-color LED display, its control system mostly uses ARM, CPLD, PAG and other chips. , The cost of a full-color screen is relatively high, the technology is relatively complicated, and the requirements for the quality of the hardware are relatively strict. But the monochromatic LED display screen is not the case, because the monochromatic LED display screen is mainly used in common facade signs, etc., the hardware requirements of the control system are relatively loose. The following is a breakdown of the hardware design of the LED display control system.
The STC89C52 single-chip microcomputer is a single-chip microcomputer of Hongjing Technology, which is compatible with the 8051 single-chip microcomputer and has many improvements. It is an enhanced 51 single-chip microcomputer. It has the following advantages with the original 51 single chip microcomputer:
1. The program written by the single-chip microcomputer cannot be read, so that the confidentiality of the production port is good.
2. Wide voltage, not afraid of power jitter.
3. Wide temperature range, -40 to 85 degrees.
4. The I/O port has been specially processed and has strong anti-interference ability.
5. The power supply system inside the single chip microcomputer has been specially processed.
6. The reset circuit inside the single-chip microcomputer is specially processed and does not require an external re-pull circuit.
7. The watchdog inside the single-chip microcomputer is specially processed, so that the program is not afraid of running away.
8. Optional 6 clock cycle/per machine cycle working mode to improve working speed.
9. The oscillation gain can be reduced to 1/2 of the original.
10. In system programming, expensive emulators and programmers are no longer needed.
11. With P4 port, increase the number of IO.
12. The speed is fast, and the frequency of the crystal oscillator can reach 80M. If the 6 times speed is used again, the frequency is equivalent to the 160M of the ordinary 8051. It is more convenient to use. The specific usage method can be found in its data manual.
SST39SF040 is a FLASH chip with 512K×8 capacity, it has 100,000 erasing cycles and 100 years of data retention time. It has a small capacity page of 4K per page, which can be page erased and chip erased, making it more convenient to use. See its data manual for specific usage.
STC62WV256 has a wide range of working voltage and a data capacity of 32K×8, and its use is the same as general RAM. See its data sheet for details.
Communication part: As an LED display control system communication, there should be two independent communication ports, that is, two serial ports. And the single-chip microcomputer I chose has only one serial port, so one serial port should be used as two serial ports accordingly. This will bring about task competition and allocation problems. In this design, a hardware switch is set up externally to use two serial ports. One for switching of external tasks, one for receiving data communication from an external computer. One is used to send data to the external display. The hardware switch uses the 74HC125 chip, 74HC125 is a three-state output high-effective four-bus buffer gate, the design is shown in U6 in this schematic diagram. Communication with an external computer requires level conversion. In this design, based on the low-cost design principle, a 232 chip is used, but a triode is used for level conversion. This alone can save more than 4 yuan in cost. The design principle is shown in the Q1 and Q2 parts.
LED display output part: This part is mainly responsible for the perfect transmission of the data sent from the serial port to the LED display. The data sent from a serial port must be sent to each line of the display screen, which requires a corresponding decoding control circuit. Finish, generally this part of the circuit is completed in two parts. In the control part, only the data line and clock line are separated. Each pair of data line and clock line separated can control 16 lines of display code on the display screen. And the circuit part that controls the control line of each row is put on the display screen. So here we mainly introduce the control part of the control system. A pair of data comes out of the single-chip microcomputer and then divided into 8 pairs of data lines and control lines through 4 pieces of 74HC125, so that this control system can control a 16×8 height display screen. The decoding line of the 16th row of the page only needs to draw 4 wires from the control system, and these 4 wires will be translated into a 16-choose 1 row control line after being on the display screen. The data latch line and the display enable line are also led out to the display screen. With these control lines and data, the entire LED display can be controlled. And this control system can control the LED display screen with a height of 16×8 and a width of 1024 dots. This part of the circuit is shown in U5, U7, U8, U9, U10 in the schematic diagram.
Storage part: The storage part is divided into two parts, one is used for the storage of the display code of the LED display screen, and the other is used for the storage of the temporary display code. The display code memory uses SST39SF040, which is a FLASH chip, and the data will not be lost after power down. According to the calculation of 32 bytes of a Chinese character, the system can store 16,384 Chinese characters. Temporary display code memory uses STC62C256 memory, which is a RAM chip, and the data is lost when power is off. It is used to save the data at the time of display. This part of the circuit is shown in U2, U3, U4 in the schematic diagram.
This control system has also added a clock chip, which can be used in places where there is a time display requirement.
All the chips used above are SMD packages to reduce the area of the circuit board and reduce the cost of hardware design.
Because of cost considerations everywhere, this control system does not have the hardware lineup of a general system. But although the product is small and complete, this control system can also complete the task of LED display control.
The hard design of the LED display control system is also derived from the environmental requirements of the product use environment. Full-color LED displays are mostly used outdoors. The outdoor environment needs to face harsh conditions such as wind, sun, rain or snow. Such outdoor use environment makes the hardware design of the full-color LED display control system relatively strict. , The hardware design of the LED display control system is also determined in accordance with the needs of the market.
