AN3114 datasheet(27/43 Pages) STMICROELECTRONICS

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AN3114

Displaying alphanumeric characters on the LCD glass

Doc ID 16829 Rev 3

27/43

Figure 18.

PD-878 physical connection for an alphanumeric character

To be able to make an efficient LCD software driver and optimize LCD alphanumeric

character coding in terms of code density, the matrix shown in Figure 19 has been chosen.

Figure 19.

PD-878 segment driver matrix

Each matrix M element corresponds to one bit on the LCD_RAM[13:0] registers. To enable

SEG(i) connected to COM(j), the “M[i][j]” element must be set to 1 and to disable it the

“M[i][j]” element must be set to 0.

The following structure provided in the LCD firmware allows to translate alphanumeric

characters from ASCII to LCD_RAM[13:0] registers:

bit[15:0] = Nibble[3:0] = {LCD_RAM[13:10], LCD_RAM[10:7],

LCD_RAM[6:3], LCD_RAM[3:0]};

Bit[15:0] are the 16 matrix terms arranged so that each nibble is related to one or several

LCD_RAM registers. The relation between the nibbles and the LCD_RAM registers is

conditioned by the LCD digit which is accessed. Table 3 summarizes the correspondence

between LCD_RAM register bits (nibble) and LCD character.

AN3114 Datasheet(PDF) 27 Page - STMicroelectronics