Hardware Reference
In-Depth Information
COM 16
DB7
LCDP (FRD7069)
DB0
Controller
LSI
HD44780U
E
R/W
RS
V
EE
V
CC
V
SS
SEG 40
SEG 160
4
Segment driver × 4
Figure 7.27
■
Block diagram of an HD44780U-based LCD kit
Pin No.
Symbol
I/0
Function
1
2
3
4
5
6
7
8
9
10
11
12
13
14
V
SS
V
CC
V
EE
R
S
R/W
E
DB0
DB1
DB2
DB3
DB4
DB5
DB6
DB7
—
—
—
I
I
I
1/0
1/0
1/0
1/0
1/0
1/0
1/0
1/0
Power supply (GND)
Power supply (
1
5 V)
Contrast adjust
0
5
instruction input, 1
5
data input
0
5
write to LCD, 1
5
read from LCD
Enable signal
Data bus line 0
Data bus line 1
Data bus line 2
Data bus line 3
Data bus line 4
Data bus line 5
Data bus line 6
Data bus line 7
Table 7.3
■
Pin assignment for displays with less than 80 characters
Otherwise, the
instruction register
is selected. The
V
EE
pin is used to control the brightness of
the display and is often connected to a potentiometer. The
V
EE
input should not be set to the
maximum value (5
V
CC
) for an extended period of time to avoid burning the LCD.
An LCD module can be used as a memory-mapped device and be enabled by an address
decoder. The E signal is normally connected to the address decoder output qualified by other
control signals to meet the timing requirement. The R/W pin can be connected to the same pin
of the microcontroller. The RS pin can be connected to the least significant bit of the address
pin (A0) from the microcontroller. This approach is applicable only for those microcontrollers
that support external memory. The LCD programming in this approach is generally easier and
more straightforward.
An LCD module can also be interfaced directly with an I/O port. In this configuration, the
designer will need to use I/O pins to control the signals E, R/W, and RS. Programming will be
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