This MAX7219 Microcontroller 4-in-1 Display Dot Matrix Module is an integrated serial input/output common-cathode display driver, it connects the microprocessor 7-segment digital LED display with 8 digits, you can also connect a bar graph display or 64 independent LED. Including a B-type BCD encoder chip, multi-channel scanning loop segment word driver, but also a static RAM 8 x 8 for storing each data. Only one external register is used to set the segment current of each LED.