ATmega162 datasheet(141/324 Pages) ATMEL

141 / 324 page

141

2513K–AVR–07/09

ATmega162/V

Figure 61. Output Compare Unit, Block Diagram

The OCR2 Register is double buffered when using any of the Pulse Width Modulation (PWM)

modes. For the normal and Clear Timer on Compare (CTC) modes of operation, the double buff-

ering is disabled. The double buffering synchronizes the update of the OCR2 Compare Register

to either top or bottom of the counting sequence. The synchronization prevents the occurrence

of odd-length, non-symmetrical PWM pulses, thereby making the output glitch-free.

The OCR2 Register access may seem complex, but this is not case. When the double buffering

is enabled, the CPU has access to the OCR2 Buffer Register, and if double buffering is disabled

the CPU will access the OCR2 directly.

Force Output

Compare

In non-PWM waveform generation modes, the match output of the comparator can be forced by

writing a one to the Force Output Compare (FOC2) bit. Forcing Compare Match will not set the

OCF2 Flag or reload/clear the timer, but the OC2 pin will be updated as if a real Compare Match

had occurred (the COM21:0 bits settings define whether the OC2 pin is set, cleared or toggled).

Compare Match

Blocking by TCNT2

Write

All CPU write operations to the TCNT2 Register will block any Compare Match that occurs in the

next timer clock cycle, even when the timer is stopped. This feature allows OCR2 to be initialized

to the same value as TCNT2 without triggering an interrupt when the Timer/Counter clock is

enabled.

Using the Output

Compare Unit

Since writing TCNT2 in any mode of operation will block all compare matches for one timer clock

cycle, there are risks involved when changing TCNT2 when using the output compare channel,

independently of whether the Timer/Counter is running or not. If the value written to TCNT2

equals the OCR2 value, the Compare Match will be missed, resulting in incorrect Waveform

Generation. Similarly, do not write the TCNT2 value equal to BOTTOM when the counter is

down-counting.

OCFn (Int.Req.)

= (8-bit Comparator )

OCRn

OCxy

DATA BUS

TCNTn

WGMn1:0

Waveform Generator

top

FOCn

COMn1:0

bottom

ATmega162 датащи(PDF) 141 Page - ATMEL Corporation

ATmega162 датащи(HTML) 141 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