HD44780U
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 (ADD) 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.
High order
bits
Low order
bits
Example: DDRAM address 4E
AC
1
0
0
1
1
1
0
AC6AC5 AC4 AC3AC2 AC1AC0
(hexadecimal)
Figure 1 DDRAM Address
Display position
(digit)
1
2
3
4
5
79
80
DDRAM
address
. . . . . . . . . . . . . . . . . .
00 01 02 03 04
4E 4F
(hexadecimal)
Figure 2 1-Line Display
Display
position
1
2
3
4
5
6
7
8
DDRAM
address
00 01 02 03 04 05 06 07
For
shift left
01 02 03 04 05 06 07 08
4F 00 01 02 03 04 05 06
For
shift right
Figure 3 1-Line by 8-Character Display Example
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HITACHI [ HITACHI SEMICONDUCTOR ]
