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Fujitsu Semiconductor (Shanghai) Co., Ltd.
Application Note
MCU-AN-500074-E-13
F²MC-8FX FAMILY
8-BIT MICROCONTROLLER
ALL SERIES
LOW POWER CONSUMPTION
STRATEGY
APPLICATION NOTE
Low Power Consumption Strategy V1.3
Revision History
Revision History
Date
2009-12-07
2009-01-08
2009-01-12
2009-01-14
Author
Edison, Zhang
Jacky, Zhou
Jacky, Zhou
Jacky, Zhou
Change of Records
V1.0, First draft
V1.1, add detail description
V1.2, add 3.3.4
V1.3, update incorrect expression
This manual contains 18 pages.
1. The products described in this manual and the specifications thereof may be changed without prior notice.
To obtain up-to-date information and/or specifications, contact your Fujitsu sales representative or Fujitsu
authorized dealer.
2. Fujitsu will not be liable for infringement of copyright, industrial property right, or other rights of a third party
caused by the use of information or drawings described in this manual.
3. The contents of this manual may not be transferred or copied without the express permission of Fujitsu.
4. The products contained in this document are not intended for use with equipment which require extremely
high reliability such as aerospace equipment, undersea repeaters, nuclear control systems or medical
equipment for life support.
5. Some of the products described in this manual may be strategic materials (or special technology) as defined
by the Foreign Exchange and Foreign Trade Control Law. In such cases, the products or portions theory
must not be exported without permission as defined under the law.
© 2009 Fujitsu Semiconductor (Shanghai) Co., Ltd.
MCU-AN-500074-E-13 – Page 2
Low Power Consumption Strategy V1.3
CONTENTS
CONTENTS
REVISION HISTORY .............................................................................................................. 2 CONTENTS ............................................................................................................................ 3 1 INTRODUCTION ................................................................................................................ 4 2 LOW POWER CONSUMPTION STRATEGY .................................................................... 5 3 HW STRATEGY ................................................................................................................. 6 3.1 Select Low Power Supply Voltage ............................................................................ 6 3.2 Select Low Power Consumption Clock ..................................................................... 7 3.2.1 Adopt Suitable Clock ................................................................................... 7 3.2.2 Switch among Clock Modes ........................................................................ 7 3.3 Select Low Power Consumption Mode ................................................................... 10 3.3.1 Internal Operating States for Standby Mode and Clock Mode .................. 10 3.3.2 Power Consumption of Standby Modes .................................................... 11 3.3.3 Switch among Different Standby Modes ................................................... 12 3.3.4 Clock Setting Example for Low Power Consumption ..................................... 13 4 SOFTWARE STRATEGY ................................................................................................ 14 4.1 Interrupt Instead of Inquire ...................................................................................... 14 4.2 Macro Instead of Subroutine ................................................................................... 14 4.3 Reduce Calculation ................................................................................................. 15 4.3.1 Inquire Table ............................................................................................. 15 4.3.2 Stop calculation when precision is satisfied .............................................. 15 4.3.3 Adopt Suitable Data Type ......................................................................... 15 4.3.4 Adopt Fujitsu Math API ............................................................................. 15 4.4 Close unused Module ............................................................................................. 16 5 ADDITIONAL INFORMATION ......................................................................................... 17 6 APPENDIX ....................................................................................................................... 18 6.1 List of Figures and Tables ....................................................................................... 18 MCU-AN-500074-E-13 – Page 3
Low Power Consumption Strategy V1.3
Chapter 1 Introduction
1 Introduction
This application note describes strategy for low power consumption in all F²MC-8FX Family
8-Bit Microcontroller Series MCU.
This application note mainly introduces method to reduce power consumption and provides
investigation of LPC MCU power consumption.
MCU-AN-500074-E-13 – Page 4
Low Power Consumption Strategy V1.3
Chapter 2 Low Power Consumption Strategy
2 Low Power Consumption Strategy
Low power consumption mainly targets to reduce system cost and increase battery life in the
embedded application, especially for portable device. For embedded application based on
MCU, minimizing system power consumption can be implemented by both hardware and
software method.
MCU-AN-500074-E-13 – Page 5
Low Power Consumption Strategy V1.3
Chapter 3 HW Strategy
3 HW Strategy
3.1
Select Low Power Supply Voltage
The power consumption can be implemented efficiently by reducing the power supply
voltage of MCU. According to LPC MCU, it can work at a wide voltage range between 2.4V
and 5.5V, as shown in Table 3-1.
Table 3-1 Operation Conditions Description
Value
Unit
Parameter
Remarks
Symbol
Power supply
voltage
VCC
Operating
temperature
TA
Min
Max
2.4
5.5
2.3
5.5
2.9
5.5
In normal
operation
2.3
5.5
Hold condition in
stop mode
-40
+85
+5
+35
In normal
operation
V
℃
Hold condition in
stop mode
Other than onchip debug
mode
On-chip debug
mode
Other than on-chip debug function
On-chip debug function
System current will be reduced largely if low power supply is adopted, and the lower the
power supply voltage is, the lower the power consumption will be. Therefore it’s better to
select lower power supply voltage only if system requirement can be achieved.
Now, power supply voltage of many MCU systems is 5V, in the last 5 years, quantity of 3V
MCU system is increasing so much, quantity of 2V MCU system is also increasing, in future,
quantity of low power supply voltage MCU system may be more than 5V. It’s an important
trend to reduce the power supply voltage of MCU.
MCU-AN-500074-E-13 – Page 6
Low Power Consumption Strategy V1.3
Chapter 3 HW Strategy
3.2
Select Low Power Consumption Clock
3.2.1 Adopt Suitable Clock
For F²MC-8FX Family 8-Bit Microcontroller Series MCU, four kinds of clock source are
available: Main clock, Main CR clock, Sub clock, Sub CR clock.
■ Main Clock Mode
Main clock is used as the machine clock for the CPU and peripheral functions. The timebase
timer operates using the main clock. The watch prescaler operates with the subclock (on the
dual external clock product).
■ Sub Clock Mode (on Dual External Clock Product)
Main clock oscillation is stopped and the sub clock is used as the machine clock for the CPU
and peripheral functions. In this mode, the timebase timer stops as it requires the main clock
for operation.
■ Main CR Clock Mode
Main CR clock is used as the machine clock for the CPU and peripheral functions. The
timebase timer and the watchdog timer operate using the main clock. The watch prescaler
operates with the sub clock (on the dual external clock product).
■ Sub CR Clock Mode (on Dual External Clock Product)
Main clock oscillation is stopped and the sub-CR clock is used as the machine clock for the
CPU and peripheral functions. In this mode, the timebase timer stops as it requires the main
clock for operation. The watch prescaler operates using the sub-CR clock.
Using Main CR clock and Sub CR clock, the advantage is to economize external crystal, so
it can reduce HW cost; the disadvantage is that the precision may be not high, and the
power consumption may be high. For more details about how to select suitable clock, refer
to related hardware manual and datasheet.
3.2.2 Switch among Clock Modes
Sometimes, it may not satisfy requirement of system function and low power consumption if
just adopting one clock mode. Therefore all four clock modes or part of four clock modes can
be adopted by Fujitsu MCU, and MCU can switch among these modes to satisfy different
requirements. Figure 3-1 and Figure 3-2 show switching between these modes.
MCU-AN-500074-E-13 – Page 7
Low Power Consumption Strategy V1.3
Chapter 3 HW Strategy
Figure 3-1 Clock Mode State Transition Diagram (Dual External Clock Product)
MCU-AN-500074-E-13 – Page 8
Low Power Consumption Strategy V1.3
Chapter 3 HW Strategy
Figure 3-2 Clock Mode State Transition Diagram (Single External Clock Product)
MCU-AN-500074-E-13 – Page 9
Low Power Consumption Strategy V1.3
Chapter 3 HW Strategy
3.3
Select Low Power Consumption Mode
For F²MC-8FX Family 8-Bit Microcontroller Series MCU, low power consumption mode
(Standby mode), includes sleep mode, timebase timer mode, watch mode and stop mode.
Power consumption in standby mode is less than in run mode.
MCU can be simply divided into below modules: main clock, main CR clock, sub clock, sub
CR clock, CPU, ROM, RAM, I/O ports, timebase timer, watch prescaler, external interrupt,
hardware watchdog timer, software watchdog timer, low-voltage detection reset, and other
peripheral Functions.
3.3.1 Internal Operating States for Standby Mode and Clock Mode
When all these modules are working, the power consumption is the highest. In run mode,
many of these modules are working, so the power consumption is high. Oppositely in
standby mode, just parts of these modules are working, so the power consumption is low.
Take MB95200/210 Series for example, Table 3-2 and Table 3-3 show operation states of
different clock modes in both RUN and sleep mode.
Table 3-2 Combinations of Standby Mode and Clock Mode and Internal Operating States (1)
MCU-AN-500074-E-13 – Page 10
Low Power Consumption Strategy V1.3
Chapter 3 HW Strategy
Table 3-3 Combinations of Standby Mode and Clock Mode and Internal Operating States (2)
3.3.2 Power Consumption of Standby Modes
Take MB95F264 as example, the power consumption is not the same in different standby
modes. Table 3-4 describes the power consumption of standby modes.
Mode Name
Table 3-4 Power Consumption of Standby Modes
Voltage
Clock Frequency
Power Consumption
Temperature
Typ
Max
Sleep mode
5.5 mA
9 mA
5.5 VCC
32MHz
+25℃
Stop mode
3.5μA
22.5μA
5.5 VCC
32kHz
+25℃
Timebase timer
mode
1.1 mA
3 mA
5.5 VCC
32MHz
+25℃
5μA
30μA
5.5 VCC
32kHz
+25℃
Watch mode
MCU-AN-500074-E-13 – Page 11
Low Power Consumption Strategy V1.3
Chapter 3 HW Strategy
3.3.3 Switch among Different Standby Modes
Sometimes, it may not satisfy requirement of system function and low power consumption if
just adopting one standby mode. So except run mode, all four standby modes or part of four
clock modes can be adopted, and MCU can switch among these modes to satisfy different
requirements. Figure 3-3 and figure 3-4 show switching between these modes.
Figure 3-3 Standby Mode State Transition Diagram (Dual External Clock Product)
MCU-AN-500074-E-13 – Page 12
Low Power Consumption Strategy V1.3
Chapter 3 HW Strategy
Figure 3-4 Standby Mode State Transition Diagram (Single External Clock Product)
3.3.4 Clock Setting Example for Low Power Consumption
Following are two simple examples:
In car alarm, select main clock as MCLK when it works at normal status, and change to sub
clock (32.768 KHz) when it enters into sleep mode.
In smoke detector or other low frequency system, select a 200K sub CR as MCLK is enough.
It is based on the fact that this kind of system only needs to work at very low frequency and
doesn’t care real time function.
MCU-AN-500074-E-13 – Page 13
Low Power Consumption Strategy V1.3
Chapter 4 Software Strategy
4 Software Strategy
Suitable software can reduce power consumption, but it’s easy to ignore by users. For
reducing power consumption, it’s not easy to find the defect on FW, and there is no strict
standard to judge if FW has the feature of low power consumption. However, there are some
ways to avoid unnecessary power consumption due to FW defect.
4.1
Interrupt Instead of Inquire
For a simple application, it doesn’t matter to adopt interrupting or inquiring, however it’s
important for lower power consumption system. When using interrupt, CPU needs to do
nothing, even enter stop mode (lowest power consumption mode); while using inquire, CPU
must access I/O registers continuously, so more additional power is consumed.
4.2
Macro Instead of Subroutine
It’s well known that more power is consumed to access RAM than to access Flash. When
using subroutine, four steps are necessary:
1 Store parameters in stack
2 Save registers in stack
3 Save result
4 Restore registers
What’s more, all these four steps are to access RAM. To solve this problem, macro can be
used instead of subroutine. In this way, the four steps to access RAM are not implemented
any more. But there is a problem that the code size is increased. Fortunately for F²MC-8FX
Family 8-Bit Microcontroller Series MCU, the Flash size is from 4K bytes to 60K bytes, and
diversified MCU can be selected to satisfy different applications.
MCU-AN-500074-E-13 – Page 14
Low Power Consumption Strategy V1.3
Chapter 4 Software Strategy
4.3
Reduce Calculation
There are many ways to reduce MCU calculation.
4.3.1 Inquire Table
Get the calculation data results beforehand, make them into a data table, and store the data
table in Flash of MCU, then MCU will get them by inquiring the data table. In this way, many
real time calculations will be reduced, so the power consumption is reduced.
4.3.2 Stop calculation when precision is satisfied
Sometimes some real time calculations must be implemented, if there is requirement for
precision, stop the calculation when the precision is satisfied. In this way, many unnecessary
real time calculations will be reduced, so the power consumption is reduced.
4.3.3 Adopt Suitable Data Type
Try to adopt suitable data type, such as using 8 bit data to instead of 16 bit data, using
fraction calculation to instead of float data calculation. In this way, some unnecessary
calculations will be reduced, so the power consumption is reduced.
4.3.4 Adopt Fujitsu Math API
Try to adopt Fujitsu Math API instead of original Fujitsu Math Lib.
Fujitsu Math APIs are available, which can be applied to all series F²MC-8FX 8-Bit
Microcontroller. This math API can calculate more efficiently. Compared to F²MC-8FX
compiler’s math arithmetic, only multiplication and division APIs which need to be advanced
are implemented in this Math API.
For details, refer to mcu-an-500073-e-14 and related sample project.
Table 4-1 shows the performance of Fujitsu Math API. In this way, many unnecessary
calculations will be reduced, so the power consumption is reduced.
Table 4-1: Performance Compare between Math API and C Compiler Math Lib
C compiler Math Lib
Calculation
Times MCLK ROM RAM
UChar*Uint
10
252
127
10
UInt*Uint
10
252
127
10
ULong*Uchar
10
252
127
10
ULong*Uint
10
252
127
10
ULong/Uchar
0
1614
238
12
ULong/Uint
0
1614
238
12
Times
2
4
4
7
0
0
Math API
MCLK
ROM
87
40
168
88
157
79
212
107
1327
80
1320
76
Note:
1 Times: how many times math API uses MULU/DIVU
2 MCLK: how many machine clock used by math API
3 ROM: how many bytes ROM used by math API
4 RAM: how many bytes RAM (stack) used by math API
MCU-AN-500074-E-13 – Page 15
RAM
8
10
12
12
12
12
Low Power Consumption Strategy V1.3
Chapter 4 Software Strategy
4.4
Close unused Module
To reduce power consumption, close MCU I/Os and periphery which are not used, and close
MCU I/Os and periphery in time which are used discontinuity.
Some periphery modules such as RS232 modules, it will cost power, so 1 I/O pin can be
used to control it, when module is not used sometimes, power of module can be turned off
by MCU.
Set unused I/O pins to input or output, and pull up to Vcc through pull up resistance,
because if these pins are not initialized, the leak current will be increased.
MCU-AN-500074-E-13 – Page 16
Low Power Consumption Strategy V1.3
Chapter 5 Additional Information
5 Additional Information
For more Information on FUJITSU Semiconductor products, visit the following web sites:
English version:
http://www.fujitsu.com/cn/fsp/services/mcu/mb95/application_notes.html
Simplified Chinese Version:
http://www.fujitsu.com/cn/fss/services/mcu/mb95/application_notes.html
MCU-AN-500074-E-13 – Page 17
Low Power Consumption Strategy V1.3
Chapter 6 Appendix
6 Appendix
6.1
List of Figures and Tables
Figure 3-1 Clock Mode State Transition Diagram (Dual External Clock Product).................... 8 Figure 3-2 Clock Mode State Transition Diagram (Single External Clock Product) ................. 9 Figure 3-3 Standby Mode State Transition Diagram (Dual External Clock Product) ............. 12 Figure 3-4 Standby Mode State Transition Diagram (Single External Clock Product) ........... 13 Table 3-1 Operation Conditions Description ............................................................................ 6 Table 3-2 Combinations of Standby Mode and Clock Mode and Internal Operating States
(1) ............................................................................................................................. 10 Table 3-3 Combinations of Standby Mode and Clock Mode and Internal Operating States
(2) ............................................................................................................................. 11 Table 3-4 Power Consumption of Standby Modes ............................................................... 11 Table 4-1: Performance Compare between Math API and C Compiler Math Lib .................. 15 MCU-AN-500074-E-13 – Page 18
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