APPENDIX B POWER SAVING
S1C17M20/M21/M22/M23/M24/M25
Seiko Epson Corporation
AP-B-1
TECHNICAL MANUAL (Rev. 1.0)
Appendix B Power Saving
Current consumption will vary dramatically, depending on CPU operating mode, operation clock frequency, periph-
eral circuits being operated, and power generator operating mode. Listed below are the control methods for saving
power.
B.1 Operating Status Configuration Examples for Power Saving
Table B.1.1 lists typical examples of operating status configuration with consideration given to power saving.
Table B.1.1 Typical Operating Status Configuration Examples
Operating status
configuration
Current
consumption
V
D1
OSC1
IOSC/
OSC3/
EXOSC
RTCA
CPU
Current consumption
listed in electrical
characteristics
Standby
↑
Low
High
↓
Economy
OFF
OFF
OFF
SLEEP
I
SLP
Clock counting
ON
ON
SLEEP or HALT
I
HALT2
Low-speed processing
OSC1 RUN
I
RUN2
Peripheral circuit operations
Normal
ON
SLEEP or HALT
I
HALT1
High-speed processing
IOSC/OSC3/EXOSC
RUN
I
RUN1
If the current consumption order by the operating status configuration shown in Table B.1.1 is different from one
that is listed in “Electrical Characteristics,” check the settings shown below.
PWGVD1CTL.REGMODE[1:0] bits of the power generator
If the PWGVD1CTL.REGMODE[1:0] bits of the power generator is 0x2 (normal mode) when the CPU enters
SLEEP mode, current consumption in SLEEP mode will be larger than I
SLP
that is listed in “Electrical Charac-
teristics.” Set the PWGVD1CTL.REGMODE[1:0] bits to 0x3 (economy mode) or 0x0 (automatic mode) before
executing the slp instruction.
CLGOSC.IOSCSLPC/OSC1SLPC/OSC3SLPC/EXOSCSLPC bits of the clock generator
Setting the CLGOSC.IOSCSLPC, OSC1SLPC, OSC3SLPC, or EXOSCSLPC bit of the clock generator to 0
disables the oscillator circuit stop control when the slp instruction is executed. To stop the oscillator circuits
during SLEEP mode, set these bits to 1.
MODEN bits of the peripheral circuits
Setting the MODEN bit of each peripheral circuit to 1 starts supplying the operating clock enabling the periph-
eral circuit to operate. To reduce current consumption, set the MODEN bits of unnecessary peripheral circuits
to 0. Note that the real-time clock has no MODEN bit, therefore, current consumption does not vary if it is
counting or idle.
OSC1 (crystal) oscillator circuit configurations
The OSC1 (crystal) oscillator circuit provides some configuration items to support various crystal resonators
with ranges from cylinder type through surface-mount type. These configurations trade off current consumption
for performance as shown below.
• The lower oscillation inverter gain setting (CLGOSC1.INV1B[1:0]/INV1N[1:0] bits) decreases current con-
sumption.
• The lower OSC1 internal gate capacitance setting (CLGOSC1.CGI1[2:0] bits) decreases current consump-
tion.
• Using lower OSC1 external gate and drain capacitances decreases current consumption.
• Using a crystal resonator with lower C
L
value decreases current consumption.
However, these configurations may reduce the oscillation margin and increase the frequency error, therefore, be
sure to perform matching evaluation using the actual printed circuit board.