Contrast Control Voltage
The LCD unit has three power terminals, V
DD
,
V
SS
, and V
0
. A contrast control voltage is supplied
to the terminal V
0
. The panel is driven by the voltage
difference between V
DD
and V
O
(i.e., V
DD
- V
O
).
Figure 11 shows an example of the contrast control
voltage supply circuit, in which VR is adjusted to
obtain the best display quality.
Sample Instruction Procedures
1. 8-Bit Data Transfer with a Single-Line, 16-Char-
acter Display (Using Internal Reset).
Table 13 shows a sample operating procedure
for an LCD unit in this mode. Initially, the function
of the LCD unit must be selected by executing
the function set instruction. Up to 80 characters
may be stored in the display data RAM, and may
be displayed by using the display shift operation.
The contents of the display data RAM are not
affected by the display shift operation, and the
display/cursor home instruction enables the res-
toration of the initial display position.
2. 4-Bit Microprocessor
The LCD unit can be connected to the I/O port
of a 4-bit microprocessor. If the I/O port is not
limited, 8-bit data may be transferred between
the devices. Otherwise, 4-bit split data may be
transferred in two operations, after selecting the
4-bit data length function. For the timing wave-
form, see Figure 9. Figure 10 shows a sample
connection to an SM-200 microprocessor.
It should be noted that the busy flag check
requires a two-step operation.
3. 8-Bit Data Transfer with a Dual-Line, 16-Charac-
ter Display (Using Internal Reset).
Table 15 shows a sample operating procedure
for an LCD unit in this mode. The cursor is
automatically moved from the first line to the
second line after column 40 of the first line has
been written. In the example (Table 15), where
only 16 characters are displayed on each line,
the display data RAM address must be reset
after the 16th character has been written. When
a display shift is executed, both lines are shifted
simultaneously. When the diplay shift operation
is repeated, characters on one line are not
moved to the other line, but rather are looped
back onto the same line.
NOTE
To use the internal reset function, the power conditions
must be satisfied. Otherwise, the LCD unit must be
initialized by the execution of a series of instructions, as
shown in the Initialization by Instructions section.
LCD UNIT
LCD27-34
V
DD
V
SS
V
O
5 K
Ω
VR
+5 V
NOTE: Ground (S type: -5 V) (Depends on particular
LCD unit model-refer to device specifications)
Figure 11. Contrast Adjustment Circuit
Dot-Matrix LCD Units
24
Display Unit User’s Manual
