Epson CMOS 32-Bit Single Chip Microcomputer S1C33L03 Technical Manual page 83

The same clock source must be used for the prescaler operating clock and the CPU operating clock. Therefore,
when operating the CPU in low-speed with the OSC1 clock, the prescaler input clock must be switched
according to the CPU operating clock. In this case, in order to prevent a malfunction in the peripheral circuit,
the prescaler should be turned off before switching the CPU operating clock. After the CPU operating clock
has been switched, switch the prescaler operating clock and then turn the prescaler on.
Function
Prescaler operating clock
switch over
Power-down control of the LCD controller
The LCD controller provides the power save mode on its own. Since the power save mode can be controlled
by software, set the mode when turning the LCD display off.
Function
Power save mode
Note: The power save mode switches the LCD panel power control signal (LCDPWR) to the inactive state.
This may cause damage of the LCD panel if the clock supply to the LCD controller is stopped at the
same time.
Therefore, do not stop the clock supply for 1 frame cycles or more after setting the LCD controller to
power save mode.
S1C33L03 PRODUCT PART
Control bit
PSCDT0 (D0)/Prescaler clock select register(0x40181) OSC1 OSC3/
Control bit
LPSAVE[1:0] D([1:0])/LCDC mode register 2
(0x39FFE3)
EPSON
5 POWER-DOWN CONTROL
"1" "0" Default
OSC3/
PLL
"11" "00" Default
Normal Power Power
operation save mode save mode
A-1
A-5
PLL
A-67