Rainbow Electronics HD44780 User Manual
Page 10
HD44780U
10
Display Data RAM (DDRAM)
Display data RAM (DDRAM) stores display data represented in 8-bit character codes. Its extended
capacity is 80
×
8 bits, or 80 characters. The area in display data RAM (DDRAM) that is not used for
display can be used as general data RAM. See Figure 1 for the relationships between DDRAM addresses
and positions on the liquid crystal display.
The DDRAM address (A
DD
) is set in the address counter (AC) as hexadecimal.
•
1-line display (N = 0) (Figure 2)
When there are fewer than 80 display characters, the display begins at the head position. For
example, if using only the HD44780, 8 characters are displayed. See Figure 3.
When the display shift operation is performed, the DDRAM address shifts. See Figure 3.
AC6 AC5 AC4 AC3 AC2 AC1 AC0
1
0
0
1
1
1
0
AC
(hexadecimal)
Example: DDRAM address 4E
High order
bits
Low order
bits
Figure 1 DDRAM Address
00
01
02
03
04
4E 4F
DDRAM
address
(hexadecimal)
Display position
(digit)
1
2
3
4
5
79
80
. . . . . . . . . . . . . . . . . .
Figure 2 1-Line Display
DDRAM
address
Display
position
1
2
3
4
5
6
7
8
00 01 02 03 04 05 06 07
For
shift left
For
shift right
00 01 02 03 04 05 06
01 02 03 04 05 06 07 08
4F
Figure 3 1-Line by 8-Character Display Example