Datasheet

86
ATtiny25/45/85 [DATASHEET]
2586Q–AVR–08/2013
12.2.1 Timer/Counter1 Initialization for Asynchronous Mode
To set Timer/Counter1 in asynchronous mode first enable PLL and then wait 100 µs for PLL to stabilize. Next, poll
the PLOCK bit until it is set and then set the PCKE bit.
12.2.2 Timer/Counter1 in PWM Mode
When the PWM mode is selected, Timer/Counter1 and the Output Compare Register C - OCR1C form a dual 8-bit,
free-running and glitch-free PWM generator with outputs on the PB1(OC1A) and PB4(OC1B) pins and inverted
outputs on pins PB0(OC1A
) and PB3(OC1B). As default non-overlapping times for complementary output pairs are
zero, but they can be inserted using a Dead Time Generator (see description on page 100).
Figure 12-4. The PWM Output Pair
When the counter value match the contents of OCR1A or OCR1B, the OC1A and OC1B outputs are set or cleared
according to the COM1A1/COM1A0 or COM1B1/COM1B0 bits in the Timer/Counter1 Control Register A - TCCR1,
as shown in Table 12-1.
Timer/Counter1 acts as an up-counter, counting from $00 up to the value specified in the output compare register
OCR1C, and starting from $00 up again. A compare match with OC1C will set an overflow interrupt flag (TOV1)
after a synchronization delay following the compare event.
Note that in PWM mode, writing to the Output Compare Registers OCR1A or OCR1B, the data value is first trans-
ferred to a temporary location. The value is latched into OCR1A or OCR1B when the Timer/Counter reaches
OCR1C. This prevents the occurrence of odd-length PWM pulses (glitches) in the event of an unsynchronized
OCR1A or OCR1B. See Figure 12-5 for an example.
Table 12-1. Compare Mode Select in PWM Mode
COM1x1 COM1x0 Effect on Output Compare Pins
00
OC1x not connected.
OC1x
not connected.
01
OC1x cleared on compare match. Set whenTCNT1 = $00.
OC1x
set on compare match. Cleared when TCNT1 = $00.
10
OC1x cleared on compare match. Set when TCNT1 = $00.
OC1x
not connected.
11
OC1x Set on compare match. Cleared when TCNT1= $00.
OC1x
not connected.
PWM1x
PWM1x
x = A or B
t
non-overlap =0
t
non-overlap =0