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How to control a HD44780-based Character-LCD
(Industry-Standard-Character-LCD)
General info and code-examples
1.1. Pin assignment
The pin assignment shown in Table 1.1. is the industry standard for character
LCD-modules with a maximum of 80 characters.
The pin assignment shown in Table 1.2. is the industry standard for character
LCD-modules with more than 80 characters.
To be sure always check the manufacturers datasheet!
To locate pin 1 on a module check the manufacturers datasheet!
Table1.1., Pin assignment for <= 80
character displays
Pin
number
Symbol Level I/O Function
1 Vss - -
2 Vcc - -
3 Vee - -
4 RS 0/1 I
5 R/W 0/1 I
6 E
7 DB0 0/1 I/O
8 DB1 0/1 I/O
9 DB2 0/1 I/O
10 DB3 0/1 I/O
11 DB4 0/1 I/O
12 DB5 0/1 I/O
13 DB6 0/1 I/O
1,
1-->0
Power supply
(GND)
Power supply
(+5V)
Contrast
adjust
0 = Instruction
input
1 = Data input
0 = Write to
LCD module
1 = Read from
LCD module
I Enable signal
Data bus line
0 (LSB)
Data bus line
1
Data bus line
2
Data bus line
3
Data bus line
4
Data bus line
5
Data bus line
6
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Table1.1., Pin assignment for <= 80
character displays
Pin
number
Pin
number
Symbol Level I/O Function
14 DB7 0/1 I/O
Table 1.2., Pin assignment for > 80
character displays
Symbol Level I/O Function
1 DB7 0/1 I/O
2 DB6 0/1 I/O
3 DB5 0/1 I/O
4 DB4 0/1 I/O
5 DB3 0/1 I/O
6 DB2 0/1 I/O
7 DB1 0/1 I/O
8 DB0 0/1 I/O
9 E1
10 R/W 0/1 I
11 RS 0/1 I
12 Vee - -
13 Vss - -
14 Vcc - -
15 E2
16 n.c.
1,
1->0
1,
1->0
Data bus line
7 (MSB)
Data bus line
7 (MSB)
Data bus line
6
Data bus line
5
Data bus line
4
Data bus line
3
Data bus line
2
Data bus line
1
Data bus line
0 (LSB)
Enable signal
I
row 0 & 1
0 = Write to
LCD module
1 = Read from
LCD module
0 = Instruction
input
1 = Data input
Contrast
adjust
Power supply
(GND)
Power supply
(+5V)
Enable signal
I
row 2 & 3
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1.2. Instruction set
Table 1.3. HD44780 instruction set
Instruction
Clear display 0 0 0 0 0 0 0 0 0 1
Cursor home 0 0 0 0 0 0 0 0 1 *
Entry mode
set
Display
On/Off control
Cursor/display
shift
RS R/W DB7 DB6 DB5 DB4 DB3 DB2 DB1 DB0
0 0 0 0 0 0 0 1 I/D S
0 0 0 0 0 0 1 D C B
0 0 0 0 0 1 S/C R/L * *
Code
Description
Clears
display and
returns
cursor to
the home
position
(address 0).
Returns
cursor to
home
position
(address 0).
Also returns
display
being
shifted to
the original
position.
DDRAM
contents
remains
unchanged.
Sets cursor
move
direction
(I/D),
specifies to
shift the
display (S).
These
operations
are
performed
during data
read/write.
Sets On/Off
of all display
(D), cursor
On/Off (C)
and blink of
cursor
position
character
(B).
Sets
cursor-move
or
display-shift
(S/C), shift
Execution
time**
1.64mS
1.64mS
40uS
40uS
40uS
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Table 1.3. HD44780 instruction set
Instruction
Function set 0 0 0 0 1 DL N F * *
Set CGRAM
address
Set DDRAM
address
Read
busy-flag and
address
counter
Write to 1 0 write data Writes data 40uS
RS R/W DB7 DB6 DB5 DB4 DB3 DB2 DB1 DB0
0 0 0 1 CGRAM address
0 0 1 DDRAM address
0 1 BF CGRAM / DDRAM address
Code
Description
direction
(R/L).
DDRAM
contents
remains
unchanged.
Sets
interface
data length
(DL),
number of
display line
(N) and
character
font(F).
Sets the
CGRAM
address.
CGRAM
data is sent
and
received
after this
setting.
Sets the
DDRAM
address.
DDRAM
data is sent
and
received
after this
setting.
Reads
Busy-flag
(BF)
indicating
internal
operation is
being
performed
and reads
CGRAM or
DDRAM
address
counter
contents
(depending
on previous
instruction).
Execution
time**
40uS
40uS
40uS
0uS
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Table 1.3. HD44780 instruction set
Instruction
CGRAM or
DDRAM
Read from
CGRAM or
DDRAM
Remarks:
- DDRAM = Display Data RAM.
- CGRAM = Character Generator RAM.
- DDRAM address corresponds to cursor position.
- * = Don't care.
- ** = Based on Fosc = 250KHz.
Bit
name
I/D
S/C 0 = Move cursor 1 = Shift display
R/L 0 = Shift left 1 = Shift right
DL 0 = 4-bit interface 1 = 8-bit interface
BF
0 = Decrement
cursor position
S 0 = No display shift 1 = Display shift
D 0 = Display off 1 = Display on
C 0 = Cursor off 1 = Cursor on
B 0 = Cursor blink off 1 = Cursor blink on
0 = 1/8 or 1/11 Duty
N
(1 line)
F 0 = 5x7 dots 1 = 5x10 dots
0 = Can accept
instruction
RS R/W DB7 DB6 DB5 DB4 DB3 DB2 DB1 DB0
1 1 read data
Table1.4. Bit names
Settings
1 = Increment cursor
position
1 = 1/16 Duty (2 lines)
1 = Internal operation
in progress
Code
Description
to CGRAM
or DDRAM.
Reads data
from
CGRAM or
DDRAM.
Execution
time**
40uS
1.3. Visible DDRAM addresses
1.3.1. 1-line displays
Shown after reset (with N=0).
Table1.5. DDRAM address usage for a 1-line LCD
Display size
Character positions DDRAM addresses
1*8 00..07 00h..07h
1*16 00..15 00h..0Fh
Visible
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Table1.5. DDRAM address usage for a 1-line LCD
Display size
Character positions DDRAM addresses
1*20 00..19 00h..13h
1*24 00..23 00h..17h
1*32 00..31 00h..1Fh
1*40 00..39 00h..27h
Visible
1.3.2. 2-line displays
Shown after reset (with N=1).
Table1.6. DDRAM address usage for a 2-line LCD
Display size
Character positions DDRAM addresses
2*16 00..15 00h..0Fh + 40h..4Fh
2*20 00..19 00h..13h + 40h..53h
2*24 00..23 00h..17h + 40h..57h
2*32 00..31 00h..1Fh + 40h..5Fh
2*40 00..39 00h..27h + 40h..67h
Visible
1.3.3. 4-line displays
Shown after reset (with N=1).
Table 1.7. DDRAM address usage for a 4-line LCD
Display size
4*16 00..15 00h..0Fh + 40h..4Fh + 14h..23h + 54h..63h
4*20 00..19 00h..13h + 40h..53h + 14h..27h + 54h..67h
4*40
Character positions DDRAM addresses
(00..39) on 1st controller and
(00..39) on 2nd controller
Visible
(00h..27h + 40h..67h) on 1st controller and
(00h..27h + 40h..67h) on 2nd controller
1.4. Interfacing
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1.4.1. 8-bit interface
Example of busy flag testing using an 8-bit interface.
1.4.2. 4-bit interface
Example of busy flag testing using a 4-bit interface.
Example of data transfer using a 4-bit interface.
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1.5. Characterset for 5x7 dot font
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