User manual

...the world's most energy friendly microcontrollers
2012-04-24 - Giant Gecko Family - d0053_Rev0.96 789
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It is also possible to connect a dedicated power supply to the LCD module. The LCD external power
supply must be connected to the LCD_BEXT pin and VLCDSEL in LCD_DISPCTRL must be set. In this
mode, the voltage booster should be disabled.
Table 33.7. LCD V
LCD
VLCDSEL Mode V
LCD
0 VDD V
DD
(same as main external power)
1 VBOOST Voltage booster/External V
DD
33.3.6 VBOOST Control
The boost voltage is configurable. By programming the VBLEV bits in LCD_DISPCTRL, the boost voltage
level can be adjusted between 3.0V and 3.6V.
The boost circuit will use an update frequency given by the VBFREQ bits in CMU_LCDCTRL, see
Table 33.8 (p. 789) ). It is possible to adjust the frequency to optimize performance for all kinds of LCD
panels (large capacitors may require less frequent updates, while small capacitors may require more
frequent updates). A lower update frequency would in general lead to smaller current consumption.
Table 33.8. LCD V
BOOST
Frequency
VBFREQ V
BOOST
Update Frequency
000 LFACLK
001 LFACLK/2
010 LFACLK/4
011 LFACLK/8
100 LFACLK/16
101 LFACLK/32
110 LFACLK/64
111 LFACLK/128
33.3.7 Framerate
It is important to choose the correct framerate for the LCD display. Normally, the framerate should be
between 30 and 100 Hz. A framerate below 30 Hz may lead to flickering, while a framerate above 100
Hz may lead to ghostering and unnecessarily high power consumption.
33.3.7.1 Clock Selection and Prescaler
The LFACLK is prescaled to LFACLK
LCDpre
in the CMU. The available prescaler settings are:
• LFCLK16: LFACLK
LCDpre
= LFACLK/16
• LFCLK32: LFACLK
LCDpre
= LFACLK/32
• LFCLK64: LFACLK
LCDpre
= LFACLK/64
• LFCLK128: LFACLK
LCDpre
= LFACLK/128
In addition to selecting the correct prescaling, the clock source can be selected in the CMU.
To use this module, the LE interface clock must be enabled in CMU_HFCORECLKEN0, in addition to
the module clock.