Explain the main functions of the LED electronic display main control circuit

The host of the LED intelligent display adopts the design scheme of MCS-51 single-chip microcomputer and dual CPU shared RAM. The host circuit mainly includes main control circuit (CPU1, Hanka, etc.), shared RAM, display control circuit ((CPU2), column drive and display circuit, switching power supply. The advantage of adopting dual CPU nanostructure is that the burden of the main CPU can be greatly reduced. Reasonably allocate RAM resources and increase the scanning rate of the display circuit.

The main control circuit of the LED electronic display is referred to as the main CPU, and the 8031 ​​single-machine is used as the CPU1. Its main functions are as follows:

(1) Receiving the upper data and instructions sent by the serial communication interface, and operating the instructions, and issuing a response signal to verify the correctness of the data. The serial communication interface consists of MCl488, MCl489, with serial (RXD), serial (TXD) and level shifting functions at a transmission rate of 9600 bit/s.

(2) The CPU 1 reads the Chinese character dot matrix information from the national standard Chinese character dot matrix chip GB5199B through the I/O interface circuit, and stores it in the dynamic memory 62256. Using the 14-bit counter inside the programmable parallel interface chip 8155, the oscillation pulse can also be counted, and an interrupt is generated periodically, so that the CPU 1 monitors its own operation at all times. In order to improve the reliability of the system, software and hardware are now used to form a two-level "watch-dog". A watchdog circuit consisting of a CD4060.

The LED electronic display CD4060 is a 14-bit binary serial count divider/oscillator. Under normal circumstances, the 8031 ​​resets the CD4060 once every t1. Once the CPU1 is out of control for some reason, the CD4060 cannot be reset in time, and it will output a high level from the Q14 terminal after t2 time (t2>t1). On the other hand, it will reset the 8031 ​​and pull the CPU1 back to normal operation. On the other hand, the CD4060 is also reset, making Q14 low. R3 and C2 are differential circuits. Obviously, the watchdog has the function of a monitor and an actuator, and is one of the important measures to improve the reliability of the intelligent display.