Pin functions – Rainbow Electronics HD44780 User Manual
Page 8
HD44780U
8
Pin Functions
Signal
No. of
Lines
I/O
Device
Interfaced with
Function
RS
1
I
MPU
Selects registers.
0: Instruction register (for write) Busy flag:
address counter (for read)
1: Data register (for write and read)
R/
W
1
I
MPU
Selects read or write.
0: Write
1: Read
E
1
I
MPU
Starts data read/write.
DB4 to DB7
4
I/O
MPU
Four high order bidirectional tristate data bus
pins. Used for data transfer and receive between
the MPU and the HD44780U. DB7 can be used
as a busy flag.
DB0 to DB3
4
I/O
MPU
Four low order bidirectional tristate data bus pins.
Used for data transfer and receive between the
MPU and the HD44780U.
These pins are not used during 4-bit operation.
CL1
1
O
Extension driver
Clock to latch serial data D sent to the extension
driver
CL2
1
O
Extension driver
Clock to shift serial data D
M
1
O
Extension driver
Switch signal for converting the liquid crystal
drive waveform to AC
D
1
O
Extension driver
Character pattern data corresponding to each
segment signal
COM1 to COM16 16
O
LCD
Common signals that are not used are changed
to non-selection waveforms. COM9 to COM16
are non-selection waveforms at 1/8 duty factor
and COM12 to COM16 are non-selection
waveforms at 1/11 duty factor.
SEG1 to SEG40
40
O
LCD
Segment signals
V1 to V5
5
—
Power supply
Power supply for LCD drive
V
CC
–V5 = 11 V (max)
V
CC
, GND
2
—
Power supply
V
CC
: 2.7V to 5.5V, GND: 0V
OSC1, OSC2
2
—
Oscillation
resistor clock
When crystal oscillation is performed, a resistor
must be connected externally. When the pin input
is an external clock, it must be input to OSC1.