5. Custom characters defining and usage

How to define special character.

Example of Correspondence between HD44780 EPROM Address Data and Character Pattern (5 × 8 Dots)

If the letter shown in the picture above should be defined as a special character its definition should look like this:

static const uint8_t leter_b[8] = {16, 16, 22, 25, 17, 17, 30, 0};

What are character banks?

The HD44780 LCD controller allows the user to define up to 8 custom characters in its CGRAM (Character Generator RAM). Sometimes, these 8 characters are insufficient for the entire application's needs but may suffice for specific parts of the functionality. By loading 8 custom characters and then reloading them with different characters at different points in the code, this limitation can be managed effectively.

A character bank is a collection of up to 8 custom characters. While each bank can contain only 8 characters, multiple character banks can be defined with different combinations of custom characters. Depending on the requirements, one of these banks can be loaded into the CGRAM and switched to another bank as needed, ensuring that the LCD displays the appropriate special characters for various parts of the application.

Example of usage

Below you can find a simple example of two special characters' bank definitions:

1. Definition of special characters in lcd_hd44780_def_char.h:

   static const uint8_t Pol_e[8] = {0, 0, 14, 17, 31, 16, 14, 3};
   static const uint8_t Pol_o[8] = {2, 4, 14, 17, 17, 17, 14, 0};
   static const uint8_t Pol_s[8] = {2, 4, 14, 16, 14, 1, 30, 0};
   static const uint8_t Pol_l[8] = {12, 4, 6, 12, 4, 4, 14, 0};
   static const uint8_t Pol_c[8] = {2, 4, 14, 16, 16, 17, 14, 0};
   static const uint8_t Pol_a[8] = {0, 0, 14, 1, 15, 17, 15, 3};
   static const uint8_t Pol_n[8] = {2, 4, 22, 25, 17, 17, 17, 0};
   static const uint8_t Zn_wody[8] = {0, 0, 0, 6, 9, 2, 4, 15};
   static const uint8_t Pol_z1[8] = {4, 32, 31, 2, 4, 8, 31, 0};
   static const uint8_t Pol_z2[8] = {2, 4, 31, 2, 4, 8, 31, 0};

2. Declaration of lcd_cgram_bank_1 in lcd_hd44780_def_char.h:

   static const struct char_bank_struct lcd_cgram_bank_1 = 
   {
     Pol_e,
     Pol_o,
     Pol_s,
     Pol_l,
     Pol_c,
     Pol_a,
     Pol_n,
     Zn_wody
   };
   enum LCD_CGRAM_BANK_1
   {
     pol_e,
     pol_o,
     pol_s,
     pol_l,
     pol_c,
     pol_a,
     pol_n,
     zn_wody,
   };

3. Declaration of lcd_cgram_bank_2 in lcd_hd44780_def_char.h:

   static const struct char_bank_struct lcd_cgram_bank_1 = 
   {
     Pol_e,
     Pol_o,
     Pol_s,
     Pol_l,
     Pol_c,
     Pol_a,
     Pol_z1,
     Pol_z2
   };
   enum LCD_CGRAM_BANK_1
   {
     pol_e,
     pol_o,
     pol_s,
     pol_l,
     pol_c,
     pol_a,
     pol_z1,
     pol_z2,
   };

4. When special characters from bank_1 are needed to display content on an LCD screen, it's required to call in the code:

   lcd_load_char_bank(&lcd_cgram_bank_1);

5. When special characters from bank_2 are required to display content on an LCD screen, then it's required to call in code:

   lcd_load_char_bank(&lcd_cgram_bank_2);

Custom Character usage

To print on LCD any user character:

1. A special characters bank with the character that you would like to print need to be loaded.
   For example:

   lcd_load_char_bank(&lcd_cgram_bank_1);

2. The lcd_char or lcd_buf_char function need to be called. For example

   lcd_char(zn_wody);