The origin and principle of 12864 LCD module.

- Oct 14, 2019-

Various models of lcd module, now we are all named after its lcd point, for example 12864, it is 128 column 64 row array. Each model of the LCD module has some of its parameters, below see some of the principles of 12864 bar. 12864, each point corresponding to a binary number,1 for bright 0 for extinction. the ram that stores these lattice information is called the display data memory. 

LCD module

To display a graph or Chinese character is to write the corresponding dot matrix information to the corresponding storage unit. Of course, the lattice information of graphics or Chinese characters is designed by themselves, and the key to the problem is the relationship between the location of the display point on the LCD screen and its address in the memory. 

Since the drive circuit of most lcd modules is composed of one row driver and two row drivers, the 12864 lcd screen is actually composed of two separate left and right 64*64 lcd screens spliced together with a 512*8bits display data ram for each half screen. the left and right half screen drive circuits and memory are selected by chip select signal cs1 and cs2 respectively. The position of the display point on the 64*64 LCD screen is determined by line number (line 0~63) and column number (column 0~63). The address of a memory cell in 512*8bitsram is determined by the page address (xpage,0~7) and the column address (yaddress,0~63). Each storage unit stores the display information of 8 liquid crystal points. 

LCD module

In order to make the corresponding relationship between the position information of liquid crystal point and the storage address more intuitive, the 64*64 liquid crystal screen is divided into 8 display blocks from top to bottom 8, and each block includes 8 rows *64 columns of lattice. the 8-line lattice information in each column constitutes an 8bits binary number, which is stored in a storage unit. 

Need to note: binary high and low effective bit order and line number corresponding relationship between different merchants and different. The ram section that holds a display block is called a storage page. That is, the dot matrix information of the 64*64 LCD screen is stored in 8 storage pages,64 bytes per page, and one column (8 lines) of dot matrix information is stored per byte. so the memory cell address includes the page address (xpage,0~7) and the column address (yaddress,0~63).