According to the characteristics of PWM (pulse width modulation (PWM: (Pulse width modulation) is a very effective mode to control analog circuits by using the microprocessor's digital output), the timing of the use of ATmega128。

Counter design output PWM should pay attention to the following points: 1. First of all, according to the actual situation, the need to determine the output of the PWM frequency range, this frequency and control of the object.

such as output PWM wave to control the brightness of the lamp, because the human eye can not distinguish the frequency of more than 42Hz, so the frequency of PWM should be higher than 42Hz, otherwise the human eye will detect the flashing lights. 2. Fast PWM can be compared to the high frequency of PWM output, but the duty ratio of the adjustment accuracy is slightly worse. At this point the counter only works in one-way forward counting mode, the top value of the counter determines the frequency of PWM, and the comparison of matching registers determines the size of the duty ratio.

The calculation formula of PWM frequency is: 3. Then according to the need of PWM frequency range to determine ATmega128 (is the Atmel Company's 8-bit series SCM the highest configuration of a single chip microcomputer, the application is extremely extensive) timing/counter PWM mode of work.

AVR Timing/Counter PWM mode can be divided into fast PWM and frequency (phase) Adjustment PWM two main categories. PWM frequency = System clock frequency/(frequency factor * (1+ counter upper limit)) AVR microcontroller is 1997 by the Atmel company developed by the enhanced built-in flash RISC (reduced based on PWM (pulse width modulation (PWM: (PULSE width)

Modulation) is the use of microprocessor digital output to control analog circuits a very effective mode), in the use of ATmega128 timing/Counter design output PWM should pay attention to the following points: 1. First of all, according to the actual situation, the need to determine the output of the PWM frequency range, this frequency and control of the object.

such as output PWM wave to control the brightness of the lamp, because the human eye can not distinguish the frequency of more than 42Hz, so the frequency of PWM should be higher than 42Hz, otherwise the human eye will detect the flashing lights. 2. Fast PWM can be compared to the high frequency of PWM output, but the duty ratio of the adjustment accuracy is slightly worse. At this point the counter only works in one-way forward counting mode, the top value of the counter determines the frequency of PWM, and the comparison of matching registers determines the size of the duty ratio.

The calculation formula of PWM frequency is: 3. Then according to the need of PWM frequency range to determine ATmega128 (is the Atmel Company's 8-bit series SCM the highest configuration of a single chip microcomputer, the application is extremely extensive) timing/counter PWM mode of work.

AVR Timing/Counter PWM mode can be divided into fast PWM and frequency (phase) Adjustment PWM two main categories.

PWM frequency = System clock frequency/(frequency factor * (1+ counter upper limit)) AVR microcontroller is 1997 by the Atmel company developed by the enhanced built-in flash RISC (reduced instruction set CPU) streamlined instruction set high-speed 8-bit single-chip microcomputer. 4. Frequency (phase) Adjustment PWM mode of duty ratio is high, but the output frequency is relatively low, because at this time the counter only works in two-way counting mode. The top value of the same counter determines the frequency of the PWM, and the value of the matching register determines the duty ratio.

The calculation formula of PWM frequency is:

PWM frequency = System clock frequency/(frequency factor *2* counter upper limit)

5. The fast PWM mode is suitable for the output PWM frequency is high, but the frequency is fixed, the duty ratio regulation accuracy request is not high application. 6. The phase adjustment PWM mode is suitable for the output PWM frequency is low, but the frequency is fixed, the duty ratio adjusts the precision to require the high application.

When the duty ratio is adjusted, the phase of the PWM is changed accordingly (Phasecorrect).

7. In the PWM mode, the top value of the counter has a fixed 0xFF (8-bit t/c), 0xFF, 0x1ff, 0x3ff (16-bit t/c). 8. Frequency and phase adjustment PWM mode is suitable for the output PWM frequency is lower, the output frequency needs to change, duty ratio adjustment precision requirements high application. At this point should be noted: not only adjust the duty ratio, the PWM phase will be corresponding to change, and one but change the top value of the counter, that is, to change the output frequency of PWM,