This paper mainly introduces the characteristics of atmega48 microcontroller, and puts forward its general method of low-power design. Taking the design of timing control system as an example, it specifies the low-power design scheme of atmega48.
With the development of microelectronics and computer technology, especially the universal application of microcomputers in various fields, the indicators of power consumption, cost, volume and reliability have become important issues for designers. Especially in battery-powered devices, how to reduce device power consumption has become a top priority in design. In this paper, atmel's atmega48 microcontroller is taken as an example to introduce the general method of low-power design of single-chip microcomputer.
Atmega48 microcontroller low-power system design is the first choice is to choose the right microcontroller. The atmega48 microcontroller is an 8-bit microcontroller with outstanding features of high performance and low power consumption. Due to the use of the risc reduced instruction set structure, its instruction set is mostly single-cycle instructions, which has the characteristics of high-speed operation. At 3v power supply, the typical power-down current of atmega48 is less than 1ua when the internal watchdog is not enabled. The specific operating current is shown in Figure 1. Moreover, the single chip can work normally in the voltage range of 1.8v~5.5v, with 4k bytes of flash, 256 bytes of e2prom, and 512 bytes of sram; and built-in 6~8 way 10 bit ad conversion Timer, watchdog, three 16-bit timer/counters, real-time counter rtc with independent oscillator, and six PWM outputs. There are also five sleep modes, pin changes and interrupts that wake up mcu.
The system with the single-chip microcomputer as the core, the total energy consumption of the system is composed of the energy consumption of the single-chip microcomputer and the energy consumption of its peripheral circuits. In order to reduce the power consumption of the entire system, in addition to reducing the operating power consumption of the microcontroller itself, it is also necessary to reduce the power consumption of the peripheral circuits. For peripheral circuits, first select low-voltage low-power devices, such as lmv324 instead of the traditional lm324, sp3223eey instead of max232. Second, the CMOS device input pins cannot be left floating. If the input pin is left floating, it is easy to accumulate charge on the input pin, resulting in a large induced electromotive force, so that the pin potential is in the transition region between 0 and 1. In addition, the peripheral circuit of the microcontroller should try to avoid the use of resistive components.
The power consumption of the atmega48 microcontroller is mainly related to the system frequency, operating mode, power supply voltage and peripheral modules. It can be seen from Fig. 1 and Fig. 2 that the operating current of the atmega48 microcontroller is proportional to its operating frequency and operating voltage.
Reduce system clock frequencyPower consumption is related to the operating frequency. As the operating frequency increases, the power consumption also increases linearly. The reduction of the operating frequency of the system and the increase in the delay of the circuit result in a decrease in system performance. Therefore, when the frequency is used to reduce the power consumption of the system, a trade-off is made between energy consumption and speed.
The atmega48 clock source can be selected from the on-chip rc oscillator or from an external clock. The on-chip rc oscillator provides a calibratable 8m clock and a 128k low power oscillator. The external clock can be selected from low power crystals, full amplitude crystals and low frequency crystals. The desired clock source can be selected by programming the flash fuse bit.
Atmega48 can get the divided system clock by setting the clock prescaler register clkpr. This feature can be utilized to reduce power consumption when the required system processing power is low. The prescaler is available for all clock sources and affects the clock frequency of the cpu and all synchronous peripherals.
The clock system of the single chip microcomputer mainly includes: cpu clock, flash clock, i/o clock, asynchronous timer clock and adc clock. In most cases, these clocks do not need to work at the same time. The clock power-suppression register, prr, provides a way to terminate individual peripheral clocks to reduce power consumption. The unused peripheral modules are turned off by setting the power consumption suppression register prr to reduce the power consumption of the chip. For example, if the adc module is not used, "1" can be written to the pradi bit in the power consumption suppression register prr to turn off the adc module of the chip. At the same time, in order to reduce power consumption, modules that do not need to work can be disabled by using different sleep modes.
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