
Appendix C: Power Saving
S1C17601 TECHNICAL MANUAL
Seiko Epson Corporation
AP-37
This section describes clock systems that can be controlled via software and power-saving control details. For more
information on control registers and control methods, refer to the respective module sections.
System SLEEP (All clocks stopped)
Execute slp instruction
Execute the slp instruction when the entire system can be stopped. The CPU switches to SLEEP mode and
the system clocks stop. This also stops all peripheral circuits using clocks. Starting up the CPU from SLEEP
mode is therefore limited to startup using ports (described later).
System clocks
Clock source selection (OSC module)
Select between IOSC/OSC3 and OSC1 for the system clock source. Reduce current consumption by selecting
the OSC1 clock when low-speed processing is possible.
IOSC/OSC3 oscillation circuit stop (OSC module)
Operate the oscillation circuit comprising the system clock source. Where possible, stop the other circuit. You
can reduce current consumption by using OSC1 as the system clock and stopping the IOSC/OSC3 oscillation
circuit.
CPU clock (CCLK)
Execute the halt instruction
Execute the halt instruction when program execution by the CPU is not required—for example, when only
the display is required or for interrupt standby. The CPU switches to HALT mode and suspends operations,
but the peripheral circuits maintain the status in place at the time of the halt instruction, enabling use of
peripheral circuits for timers and interrupts. You can reduce power consumption even further by suspending
unnecessary peripheral circuits before executing the halt instruction. The CPU is started from HALT mode
using the port or interrupts from the peripheral circuit operating in HALT mode.
Low-speed clock gear selection (CLG module)
The CLG module can reduce CPU clock speeds to between 1/1 and 1/8 of the system clock via the clock gear
settings. Reduce current consumption by operating the CPU at the minimum speed required for applications.
Peripheral clock (PCLK)
PCLK stop (CLG module)
Stop the PCLK clock feed from the CLG to peripheral circuits if none of the following peripheral circuits is
required.
Peripheral circuits operating with PCLK
Prescaler (PWM timer, remote controller, P port)
UART
8-bit timer
16-bit timer Ch.0 to Ch.2
Interrupt controller
SPI
I2C (master/slave)
Power supply control circuit
P port and port MUX (control register, chattering filter)
PWM timer
MISC register
A/D converter
SVD circuit