The low power consumption of electronic products often gives product designers a headache and has to face it. The power consumption of a system with a single-chip microcomputer (MCU) as the core is mainly composed of the power consumption of the single-chip microcomputer and the power consumption of the peripheral circuit of the single-chip microcomputer. To reduce the power consumption of the microcontroller system, it is necessary to start with both hardware and software.
To meet the low-power requirements of the microcontroller system, it is easy to select a microcontroller with low-power characteristics (for example, the high-speed C8051F series microcontroller designed by Siliconlaboratories). Because a microcontroller with low power consumption can greatly reduce system power consumption, the low power consumption characteristics of a microcontroller can be investigated from the power supply voltage, internal structure, system clock, and low power mode of the microcontroller. Generally speaking, in the process of selecting technology suppliers and products, users need to make more in-depth considerations on the following important hardware parameters:
Choose a simple CPU core
When choosing a CPU core, avoid blindly pursuing performance, and follow the principle of "enough is good." If an 8-bit machine is enough, there is no need to choose a 16-bit machine or a 32-bit machine; the faster the microcontroller runs, the more power it consumes. The more complex a CPU, the higher the level of integration, the stronger the function, the more on-chip transistors, and the greater the total leakage current. Even if it enters the STOP state, the leakage current will become non-negligible; and a simple CPU core not only has low power consumption , The cost is also low.
Choose a single-chip microcomputer system with low voltage power supply
The low power supply voltage of the single chip microcomputer system can effectively reduce its system power consumption. Due to the development of the semiconductor manufacturing process, the power supply voltage of the single-chip microcomputer has been reduced from 5V to 3.3V, 3V, 2V and even 1.8V. The low power supply voltage can reduce the power consumption of the single-chip microcomputer, and can also reduce the power consumption of the peripheral circuit of the single-chip microcomputer.
Choose a single-chip microcomputer system with low power consumption mode
The low power consumption mode refers to the Idle, Stop and Suspend modes of the system. The power consumption in these modes will be much less than the power consumption under normal operation. In Idle mode, the CPU stops working, but the internal system clock does not stop, and the peripheral I/O modules of the microcontroller do not stop working; the system power consumption is generally reduced by a limited amount, which is equivalent to about 50% of the power consumption of the working mode.
If each analog peripheral is turned off when the CPU enters the Stop mode, the power consumption at this time can be reduced to nA level. But in Stop mode, the system must be re-initialized after the CPU is awakened, and the contents of all special function registers will be re-initialized. This needs attention in some low-power applications.
In the Suspend mode, the CPU and internal system clock stop working, I/O modules, etc. are suspended, the data stored in the on-chip RAM will be retained, the power consumption of the CPU can be reduced to nA level, and wake up by a wake-up event. When the CPU is awakened, the system will not be reset by the CPU, and continue to execute the program from where it entered the Suspend mode. This is a very ideal low-power mode.
At the hardware level, it is very necessary to carefully measure the above parameters. In addition, it is also very important to choose a suitable clock scheme and use the power consumption per MIPS to measure the low-power performance of the MCU.
Application software considerationsThe importance of application software design for a low-power system is often overlooked. An important reason is that defects in software design are not as easy to find as hardware, and there is no strict standard to judge the low power consumption characteristics of a software. But if the designer can reflect the application's low power consumption characteristics in the software as much as possible, he can avoid those "invisible" power losses:
Use "interrupt" instead of "query"
In situations where low power consumption is not required, it does not matter whether the program uses the interrupt mode or the query mode. But in occasions where low power consumption is required, these two methods are far apart. Using the interrupt mode, the CPU can do nothing, and even enter the wait mode or stop mode; while in the query mode, the CPU must constantly access the I/O registers, which will bring a lot of additional power consumption.
Use "macro" instead of "subroutine"
The stacking and popping operations of the subroutine call require two operations on the RAM, which will bring greater power consumption. The macro is expanded at compile time, and the CPU executes the instructions in sequence. Using macros will increase the amount of program code, but for applications that don't care about the large amount of program code, using macros will undoubtedly reduce the power consumption of the system.
Minimize the amount of CPU calculations
Reducing the computational workload of the CPU can effectively reduce the power consumption of the CPU. There are many ways to reduce the work of CPU calculations: use the table lookup method to replace real-time calculations; the inevitable real-time calculations will end when the accuracy is enough to avoid "excessive" calculations; try to use short data types, such as , Try to use 8-bit character data instead of 16-bit integer data, and try to use fractional arithmetic instead of floating-point arithmetic.
Let I/O modules run intermittently
During the operation of the system, the I/O modules that are not in use must be turned off, and the I/O modules that are used intermittently must be turned off in time to save power. At the same time, the unused I/O pins should be set as output or as input, and pulled up with a pull-up resistor.
In short, in the process of designing a single-chip microcomputer system, it is necessary to deeply understand the characteristics of low-power consumption of the single-chip microcomputer, and make full use of the low-power characteristics of the single-chip microcomputer in the design process of hardware and application software to design products that meet the requirements of low power consumption.
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