SIC63616-(Rev. 1.0) NO. P64
3240-0412
(2) Controlling the LCD system voltage regulator
To start LCD display, turn the LCD system voltage regulator on using the LPWR register. When "1"
is written to LPWR, the LCD system voltage regulator goes on and generates the LCD drive voltages
listed in Table 4.6.2.1. At initial reset, LPWR is set to "0" (Off).
When LCD display is not necessary, turn the LCD system voltage regulator off to reduce power con-
sumption.
To generate stable LCD drive voltages, the LCD system voltage regulator must be driven with a source
voltage higher than the reference voltage V
C2
or V
C1
. When a V
C2
reference voltage option (TYPE 1 or
TYPE 2) is selected, the LCD system voltage regulator can be driven with the V
D2
voltage generated by
the power supply voltage booster/halver (boost mode) if the supply voltage V
DD
is less than 2.5 V. The
V
D2
voltage is generated by approximately doubling the V
DD
voltage. Use the VCSEL register to select
V
DD
or V
D2
to drive the LCD system voltage regulator. V
DD
is selected when VCSEL is "0" and V
D2
is
selected when VCSEL is "1". When using V
D2
, the power supply voltage booster/halver must be turned
on by writing "1" to the DBON register before switching to V
D2
.
When the V
C1
reference voltage option (TYPE 3) is selected, this control is not required. In this case,
VCSEL and DBON should be set to "0".
Furthermore, the LCD system voltage regulator uses the boost clock supplied from the clock manager
for boosting/halving the voltage. The clock supply is controlled by the VCCKS0–VCCKS1 register. Set
VCCKS to "01B" before writing "1" to LPWR. When LCD display is not necessary, stop the clock supply
by setting VCCKS to "00B" to reduce power consumption.
Table 4.6.2.2 Controlling boost clock
VCCKS1
1
0
0
Boost clock control
Prohibited
On (2 kHz)
Off
VCCKS0
*
1
0
Note: The oscillation circuit stops oscillating in SLEEP mode set by the SLP instruction of the CPU.
Therefore, the power supply voltage booster/halver cannot generate V
D2
in SLEEP mode. Before
executing the SLP instruction, configure the LCD system voltage regulator (VCSEL="0", DBON="0")
so that it will be driven with V
DD
.
(3) Heavy load protection mode for LCD system voltage regulator
The LCD system voltage regulator has a heavy load protection function that can be activated with soft-
ware to stabilize display on the LCD as much as possible (to minimize degradation in display quality)
even if fluctuations in the supply voltage occur due to driving an external load. By writing "1" to the
VCHLMOD register, the LCD system voltage regulator enters heavy load protection mode to stabilize
the V
C1
to V
C5
outputs. Use the heavy load protection function if the LCD display has inconsistencies in
density when a heavy load such as a lamp or buzzer is driven with a port output. At initial reset, VCHL-
MOD is set to "0" (Off).
Note: The heavy load protection mode increases current consumption compared with normal operation
mode. Therefore, do not set heavy load protection mode unless it is necessary.
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