13. Dot Matrix LCD Controller (H8/3857 Group)
Rev.3.00 Jul. 19, 2007 page 362 of 532
REJ09B0397-0300
13.3.11 Power Supply Circuit
The LCD controller has a built-in 2X or 3X step-up circuit for LCD drive. In standby mode, the
power supply circuit is automatically turned off after a maximum of two subclock cycles, and the
power consumption of the step-up circuit falls to zero. The power supply circuit can be turned on
and off by a command, and an external power supply circuit should be used if the current capacity
of the built-in step-up circuit is insufficient.
Step-Up Circuit
By inputting the reference voltage to V
ci
(V
ci
≤
V
CC
), connecting a capacitor between V
SS
and
VLOUT, C1+ and C1–, and C2+ and C2–, and setting the PWR bit in control register 1 (LR0) to
1, the potential between V
ci
and V
CC
is stepped up by a factor of 2 or 3. See figures 13.17 (1) and
(2) for the method of connecting the capacitors. As the subclock is used for voltage step-up, step-
up will not be performed unless the subclock is supplied. Since V
ci
is also used for the step-up
circuit power supply, an adequate current must be assured.
Step-up cannot be performed below V
CC
. Apply a V
ci
voltage that gives a VLOUT level between
V
CC
and 7.0 V.
If the step-up circuit is not used, connect V
ci
to V
CC
.
LCD Drive Level Power Supply
Six power supply levels
⎯
V1, V2, V3, V3, V4, V5, and V
SS
⎯
are necessary for LCD drive. The
V1 to V
SS
power supplies are normally generated by means of resistive division. The power supply
circuit includes a voltage follower op-amp for each voltage level generated by resistive division.
When 1/4 bias is used for LCD display, the V3 and V4 pins should be shorted; when 1/5 bias is
used, the V3 and V4 pins should be left open. The V34 pin is an internal resistance test pin, and
should always be shorted to the V3 pin externally.
Contrast Control
The LCD controller provides for the following two methods of contrast control.
•
Using built-in contrast control circuit
The LCD controller includes a programmable contrast control circuit. The LCD power supply
voltage can be adjusted on the basis of a given step-up circuit voltage by making a selection in
the contrast control register (LRA).
Summary of Contents for F-ZTAT H8 Series
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