Appendix B Power Saving; Operating Status Configuration Examples For Power Saving - Epson S1C17W22 Technical Manual

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.
Operating status
configuration
Standby
Clock counting
Low-speed processing
Peripheral circuit operations
High-speed processing
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.
PWGCTL.PWGMOD[2:0] bits of the power generator
If the PWGCTL.PWGMOD[2:0] 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
teristics." Set the PWGCTL.PWGMOD[2:0] bits to 0x5 (super economy mode), 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 oscillator circuit configurations
The OSC1 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 perfor-
mance 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
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.
S1C17W22/W23 TECHNICAL MANUAL
(Rev. 1.3)
Table B.1.1 Typical Operating Status Configuration Examples
Current
PWG2 OSC1
consumption
OFF
Super
↑
economy/
Low
Economy
ON
High Normal
↓
value decreases current consumption.
L
Seiko Epson Corporation
APPENDIX B POWER SAVING
IOSC/
OSC3/ RTCA CPU
EXOSC
OFF SLEEP
OFF SLEEP or HALT
OSC1 RUN
ON SLEEP or HALT
ON IOSC/OSC3/EXOSC
RUN
that is listed in "Electrical Charac-
SLP
Current consumption
listed in electrical
characteristics
I
SLP
I
HALT2
I
RUN20
I
HALT1
I
RUN10
AP-B-1