Rainbow Electronics HD44780 - Manual (Page 16)

HD44780U
16

Handling unused character patterns
1. EPROM data outside the character pattern area: Always input 0s.
2. EPROM data in CGRAM area: Always input 0s. (Input 0s to EPROM addresses 00H to FFH.)
3. EPROM data used when the user does not use any HD44780U character pattern: According to the user
application, handled in one of the two ways listed as follows.
a. When unused character patterns are not programmed: If an unused character code is written into
DDRAM, all its dots are lit. By not programing a character pattern, all of its bits become lit. (This is
due to the EPROM being filled with 1s after it is erased.)
b. When unused character patterns are programmed as 0s: Nothing is displayed even if unused
character codes are written into DDRAM. (This is equivalent to a space.)
Table 3 Example of Correspondence between EPROM Address Data and Character Pattern
(5
×
10 Dots)
A 1 0 A 9 A 8 A 7 A 6 A 5 A 4 A 3 A 2 A 1 A 0
Data
O 4 O 3 O 2 O 1 O 0
0 0 0 1
0 0 1 0
0 0 1 1
0 1 0 0
0 1 0 1 0 0 1 0
EPROM Address
Character code Line
position
LSB
0 1 0 1
0 1 1 0
0 1 1 1
0 0 0 0 0
0 0 0 0 0
0 1 1 0 1
1 0 0 1 1
1 0 0 0 1
1 0 0 0 1
0 0 0 0
A 1 1
1 0 0 1
1 0 1 0
1 0 1 1
1 1 0 0
1 1 0 1
1 1 1 0
1 1 1 1
1 0 0 0
Cursor position 0 0 0 0 0
0 0 0 0 0
0 0 0 0 0
0 0 0 0 0
0 0 0 0 0
0 0 0 0 0
0 0 0 0 1
0 0 0 0 1
0 0 0 0 1
0 1 1 1 1
Notes: 1. EPROM addresses A11 to A3 correspond to a character code.
2. EPROM addresses A3 to A0 specify a line position of the character pattern.
3. EPROM data O4 to O0 correspond to character pattern data.
4. EPROM data O5 to O7 must be specified as 0.
5. A lit display position (black) corresponds to a 1.
6. Line 11 and the following lines must be blanked with 0s for a 5
×
10 dot character fonts.