
6 LCD POWER SEQUENCING AND POWER SAVE MODES
SID13705 PROGRAMMING NOTES
EPSON
C-2-23
AND EXAMPLES
6
LCD POWER SEQUENCING AND POWER
SAVE MODES
6.1 LCD Power Sequencing
Correct power sequencing is required to prevent long term damage to LCD panels and to avoid
unsightly" lines" during power-up and power-down. Power Sequencing allows the LCD power
supply to discharge prior to shutting down the LCD logic signals.
Proper LCD power sequencing dictates there must be a time delay between the LCD power being
disabled and the LCD signals being shut down. During power-up the LCD signals must be active
prior to or when power is applied to the LCD. The time intervals vary depending on the power
supply design.
The SID13705 block performs automatic power sequencing in response to both software power
save (REG[03h]) or in response to a hardware power save. One frame after a power save mode is
set, the SID13705 block disables LCD power, and the LCD logic signals continue for one hundred
and twenty seven frames allowing the LCD power supply to completely discharge. For most
applications the internal power sequencing is the appropriate choice.
There may be situations where the internal time delay is insufficient to discharge the LCD power
supply before the LCD signals are shut down, or the delay is too long and the designer wishes to
shorten it. This section details the sequences to manually power-up and power-down the LCD
interface.
6.2 Registers
The LCD Power (LCDPWR) Override bit forces LCD power inactive one frame after being
toggled. As long as this bit is "1" LCD power will be disabled.
The Hardware Power Save Enable bit must be set in order to activate hardware power save
through GPIO0.
The Software Power Save bits set and reset the software power save mode. These bits are set to
"11" for normal opertion and set to "00" for power save mode.
LCD logic signals to the display panel are active for 128 frames after setting either hardware or
software power save modes. Power sequencing overide is performed by setting the LCDPWR
Override bit some time before setting a power save mode for power off sequences. During power
on sequences the power save mode is reset some time before the LCDPWR Override is reset
resulting in the LCD logic signals being active before power is applied to the panel.
REG[03h] Mode Register 2
LCDPWR
Override
Hardware
Power Save
Enable
Software
Power Save
bit 1
Software
Power Save
bit 0