ATtiny167-ESSZ datasheet(123/282 Pages) ATMEL

123 / 282 page

123

7728D–AVR–07/09

ATtiny87/ATtiny167

or toggle at a compare match (See ”Compare Match Output Unit” on page 120.). The OCnxi

bits over control the setting of the COM1A/B1:0 bits as shown in Figure 12-6 on page 122.

For detailed timing information refer to “Timer/Counter Timing Diagrams” on page 130.

12.9.1

Normal Mode

The simplest mode of operation is the Normal mode (WGM13:0 = 0). In this mode the counting

direction is always up (incrementing), and no counter clear is performed. The counter simply

overruns when it passes its maximum 16-bit value (MAX = 0xFFFF) and then restarts from the

BOTTOM (0x0000). In normal operation the Timer/Counter Overflow Flag (TOV1) will be set in

the same timer clock cycle as the TCNT1 becomes zero. The TOV1 flag in this case behaves

like a 17th bit, except that it is only set, not cleared. However, combined with the timer over-

flow interrupt that automatically clears the TOV1 flag, the timer resolution can be increased by

software. There are no special cases to consider in the Normal mode, a new counter value

can be written anytime.

The Input Capture unit is easy to use in Normal mode. However, observe that the maximum

interval between the external events must not exceed the resolution of the counter. If the inter-

val between events are too long, the timer overflow interrupt or the prescaler must be used to

extend the resolution for the capture unit.

The Output Compare units can be used to generate interrupts at some given time. Using the

Output Compare to generate waveforms in Normal mode is not recommended, since this will

occupy too much of the CPU time.

12.9.2

Clear Timer on Compare Match (CTC) Mode

In Clear Timer on Compare or CTC mode (WGM13:0 = 4 or 12), the OCR1A or ICR1 Register

are used to manipulate the counter resolution. In CTC mode the counter is cleared to zero

when the counter value (TCNT1) matches either the OCR1A (WGM13:0 = 4) or the ICR1

(WGM13:0 = 12). The OCR1A or ICR1 define the top value for the counter, hence also its res-

olution. This mode allows greater control of the compare match output frequency. It also

simplifies the operation of counting external events.

The timing diagram for the CTC mode is shown in Figure 12-7. The counter value (TCNT1)

increases until a compare match occurs with either OCR1A or ICR1, and then counter

(TCNT1) is cleared.

Figure 12-7. CTC Mode, Timing Diagram

TCNTn

OCnAi

(Toggle)

OCnA Interrupt Flag Set

or ICFn Interrupt Flag Set

(Interrupt on TOP)

Period

(COMnA1:0 = 1)

ATtiny167-ESSZ датащи(PDF) 123 Page - ATMEL Corporation

ATtiny167-ESSZ 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