The 12864 dot matrix liquid crystal display module (LCM) is a 128 column * 64 line array consisting of 128*64 liquid crystal display points. Each display point corresponds to a binary number, 1 for light and 0 for off. The RAM that stores these dot information is called a display data memory. To display a graphic or Chinese character, the corresponding dot information is written to the corresponding storage unit.

The display content is to find the relationship between the position (row and column) of the displayed point on the LCD screen and its address in the memory. Since the driving circuit of most liquid crystal display modules is composed of one row driver and two column drivers, the 12864 liquid crystal panel is actually formed by splicing two independent 64*64 liquid crystal screens, and each half screen has a 512*8. Bits display data RAM.

The left and right half screen drive circuits and memories are selected by chip select signals CS1 and CS2, respectively. (In order to simplify the user design, a few manufacturers add a decoding circuit to the module, so that the 128*64 LCD screen is a full screen, only one chip select signal is needed.) The position of the display point on the 64*64 LCD screen is determined by the line number ( Line, 0~63) and column number (column, 0~63) are determined. The address of a memory location in 512*8 bits RAM is determined by the page address (Xpage, 0~7) and the column address (Yaddress, 0~63). Each storage unit stores display information of 8 liquid crystal dots.