AN3114 datasheet(35/43 Pages) STMICROELECTRONICS

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AN3114

Displaying alphanumeric characters on the LCD glass

Doc ID 16829 Rev 3

35/43

To be able to make an efficient LCD software driver and optimize the LCD character coding

in terms of code density, the matrix shown in Figure 23 has been chosen.

Figure 23.

HXO5002B 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 enables to translate alphanumeric

characters from ASCII into LCD_RAM[21:0]:

bit[17:0] = Nibble[5:0] = {LCD_RAM[13:10], LCD_RAM[10:7],

LCD_RAM[6:3], LCD_RAM[3:0],LCD_RAM[10:7], LCD_RAM[13:10]};

bit[17:0] are the 18 matrix terms arranged so that each nibble is related to LCD_RAM

LCD_RAM registers is conditioned by the LCD digit being accessed. Refer to Table 6 for the

correspondence between LCD_RAM register bits (nibble) and LCD character.

Displaying a character “A” on the custom LCD glass HXO5002B

The LCD segments A, B, C, E, F, M and N must be activated to display the “A” letter (see

Figure 24). These segments must then be transferred from the LCD_RAM registers to the

LCD glass. Use the matrix described in Figure 23 to know which bits of the LCD_RAM

registers must be set.

The firmware structure provides the value 0x002536 for Nibble[5:0] corresponding to:

●

Nibble[0] = 0x0 = 000b

●

Nibble[1] = 0x0 = 000b

●

Nibble[2] = 0x2 = 010b

●

Nibble[3] = 0x5 = 101b

●

Nibble[4] = 0x3 = 011b

●

Nibble[5] = 0x6 = 110b

AN3114 Datasheet(PDF) 35 Page - STMicroelectronics