Rainbow Electronics HD44780 User Manual

Page 13

HD44780U

Character Generator ROM (CGROM)

The character generator ROM generates 5

8 dot or 5

10 dot character patterns from 8-bit character

codes (Table 4). It can generate 208 5

8 dot character patterns and 32 5

10 dot character patterns. User-

defined character patterns are also available by mask-programmed ROM.

Character Generator RAM (CGRAM)

In the character generator RAM, the user can rewrite character patterns by program. For 5

8 dots, eight

character patterns can be written, and for 5

10 dots, four character patterns can be written.

Write into DDRAM the character codes at the addresses shown as the left column of Table 4 to show the
character patterns stored in CGRAM.

See Table 5 for the relationship between CGRAM addresses and data and display patterns.

Areas that are not used for display can be used as general data RAM.

Modifying Character Patterns

•

Character pattern development procedure

The following operations correspond to the numbers listed in Figure 7:

1. Determine the correspondence between character codes and character patterns.

2. Create a listing indicating the correspondence between EPROM addresses and data.

3. Program the character patterns into the EPROM.

4. Send the EPROM to Hitachi.

5. Computer processing on the EPROM is performed at Hitachi to create a character pattern listing, which

is sent to the user.

6. If there are no problems within the character pattern listing, a trial LSI is created at Hitachi and samples

are sent to the user for evaluation. When it is confirmed by the user that the character patterns are
correctly written, mass production of the LSI proceeds at Hitachi.