Holtek TinyPower HT69F40A Manual page 182

TinyPower
Programming Considerations
Certain precautions must be taken when programming the LCD. One of these is to ensure that
the LCD Memory is properly initialised after the microcontroller is powered on. Like the General
Purpose Data Memory, the contents of the LCD Memory are in an unknown condition after
power-on. As the contents of the LCD Memory will be mapped into the actual display, it is important
to initialise this memory area into a known condition soon after applying power to obtain a proper
display pattern.
Consideration must also be given to the capacitive load of the actual LCD used in the application.
As the load presented to the microcontroller by LCD pixels can be generally modeled as mainly
capacitive in nature, it is important that this is not excessive, a point that is particularly true in the
case of the COM lines which may be connected to many LCD pixels. The accompanying diagram
depicts the equivalent circuit of the LCD.
One additional consideration that must be taken into account is what happens when the
microcontroller enters the Idle or Slow Mode. The LCDEN control bit in the LCDC register permits
the display to be powered off to reduce power consumption. If this bit is zero, the driving signals
to the display will cease, producing a blank display pattern but reducing any power consumption
associated with the LCD.
After Power-on, note that as the LCDEN bit will be cleared to zero, the display function will be
disabled.
Rev. 1.20
HT69F30A/HT69F40A/HT69F50A
I/O Flash 8-Bit MCU with LCD & EEPROM
TM
S E G 0 S E G 1 S E G 2
C O M 0
C O M 1
C O M 2
C O M n
LCD Panel Equivalent Circuit
1�2
S E G n
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