ATmega162 datasheet(123/324 Pages) ATMEL

123 / 324 page

123

2513K–AVR–07/09

ATmega162/V

value (at TOP). The Interrupt Flags can be used to generate an interrupt each time the counter

reaches the TOP or BOTTOM value.

When changing the TOP value the program must ensure that the new TOP value is higher or

equal to the value of all of the compare registers. If the TOP value is lower than any of the com-

pare registers, a Compare Match will never occur between the TCNTn and the OCRnx. Note

that when using fixed TOP values, the unused bits are masked to zero when any of the OCRnx

Registers are written. As the third period shown in Figure 53 illustrates, changing the TOP

actively while the Timer/Counter is running in the phase correct mode can result in an unsym-

metrical output. The reason for this can be found in the time of update of the OCRnx Register.

Since the OCRnx update occurs at TOP, the PWM period starts and ends at TOP. This implies

that the length of the falling slope is determined by the previous TOP value, while the length of

the rising slope is determined by the new TOP value. When these two values differ the two

slopes of the period will differ in length. The difference in length gives the unsymmetrical result

on the output.

It is recommended to use the phase and frequency correct mode instead of the phase correct

mode when changing the TOP value while the Timer/Counter is running. When using a static

TOP value there are practically no differences between the two modes of operation.

In phase correct PWM mode, the compare units allow generation of PWM waveforms on the

OCnx pins. Setting the COMnx1:0 bits to two will produce a non-inverted PWM and an inverted

PWM output can be generated by setting the COMnx1:0 to three (See Table 55 on page 129).

The actual OCnx value will only be visible on the port pin if the data direction for the port pin is

set as output (DDR_OCnx). The PWM waveform is generated by setting (or clearing) the OCnx

clearing (or setting) the OCnx Register at Compare Match between OCRnx and TCNTn when

the counter decrements. The PWM frequency for the output when using phase correct PWM can

be calculated by the following equation:

The N variable represents the prescaler divider (1, 8, 64, 256, or 1024). For Timer/Counter3 also

prescaler factors 16 and 32 are available.

The extreme values for the OCRnx Register represent special cases when generating a PWM

waveform output in the phase correct PWM mode. If the OCRnx is set equal to BOTTOM the

output will be continuously low and if set equal to TOP the output will be continuously high for

non-inverted PWM mode. For inverted PWM the output will have the opposite logic values. If

OCRnA is used to define the TOP value (WGMn3:0 = 11) and COMnA1:0 = 1, the OCnA output

will toggle with a 50% duty cycle.

Phase and Frequency

Correct PWM Mode

The phase and frequency correct Pulse Width Modulation, or phase and frequency correct PWM

mode (WGMn3:0 = 8 or 9) provides a high resolution phase and frequency correct PWM wave-

form generation option. The phase and frequency correct PWM mode is, like the phase correct

PWM mode, based on a dual-slope operation. The counter counts repeatedly from BOTTOM

(0x0000) to TOP and then from TOP to BOTTOM. In non-inverting Compare Output mode, the

Output Compare (OCnx) is cleared on the Compare Match between TCNTn and OCRnx while

up-counting, and set on the Compare Match while down-counting. In inverting Compare Output

mode, the operation is inverted. The dual-slope operation gives a lower maximum operation fre-

quency compared to the single-slope operation. However, due to the symmetric feature of the

dual-slope PWM modes, these modes are preferred for motor control applications.

The main difference between the phase correct, and the phase and frequency correct PWM

mode is the time the OCRnx Register is updated by the OCRnx Buffer Register, (see Figure 53

and Figure 54).

fOCnxPCPWM

clk_I/O

NTOP

⋅⋅

----------------------------

ATmega162 датащи(PDF) 123 Page - ATMEL Corporation

ATmega162 датащи(HTML) 123 Page - ATMEL Corporation

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

датащи скачать

ссылки URL