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 s 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,
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
Table 12-1.
Compare Mode Select in PWM Mode
COM1x1
COM1x0
Effect on Output Compare Pins
00
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
x = A or B
t non-overlap=0