83
7598H–AVR–07/09
ATtiny25/45/85
Figure 14-3. Timer/Counter1 Block Diagram
Three status flags (overflow and compare matches) are found in the Timer/Counter Interrupt
Flag Register - TIFR. Control signals are found in the Timer/Counter Control Registers TCCR1
and GTCCR. The interrupt enable/disable settings are found in the Timer/Counter Interrupt
Mask Register - TIMSK.
The Timer/Counter1 contains three Output Compare Registers, OCR1A, OCR1B, and OCR1C
as the data source to be compared with the Timer/Counter1 contents. In normal mode the Out-
put Compare functions are operational with all three output compare registers. OCR1A
determines action on the OC1A pin (PB1), and it can generate Timer1 OC1A interrupt in normal
mode and in PWM mode. Likewise, OCR1B determines action on the OC1B pin (PB3) and it can
generate Timer1 OC1B interrupt in normal mode and in PWM mode. OCR1C holds the
Timer/Counter maximum value, i.e. the clear on compare match value. In the normal mode an
overflow interrupt (TOV1) is generated when Timer/Counter1 counts from $FF to $00, while in
the PWM mode the overflow interrupt is generated when Timer/Counter1 counts either from $FF
to $00 or from OCR1C to $00. The inverted PWM outputs OC1A and OC1B are not connected in
normal mode.
In PWM mode, OCR1A and OCR1B provide the data values against which the Timer Counter
value is compared. Upon compare match the PWM outputs (OC1A, OC1A, OC1B, OC1B) are
generated. In PWM mode, the Timer Counter counts up to the value specified in the output com-
pare register OCR1C and starts again from $00. This feature allows limiting the counter “full”
value to a specified value, lower than $FF. Together with the many prescaler options, flexible
PWM frequency selection is provided.
lists clock selection and OCR1C values to
obtain PWM frequencies from 20 kHz to 250 kHz in 10 kHz steps and from 250 kHz to 500 kHz
in 50 kHz steps. Higher PWM frequencies can be obtained at the expense of resolution.
8-BIT DATABUS
TIMER INT. FLAG
REGISTER (TIFR)
TIMER/COUNTER1
8-BIT COMPARATOR
T/C1 OUTPUT
COMPARE REGISTER
TIMER INT. MASK
REGISTER (TIMSK)
TIMER/COUNTER1
(TCNT1)
T/C CLEAR
T/C1 CONTROL
LOGIC
TOV1
OCF1B
OCF1B
TOV1
TOIE0
TOIE1
OCIE1B
OCIE1A
OCF1A
OCF1A
CK
PCK
T/C1 OVER-
FLOW IRQ
T/C1 COMPARE
MATCH B IRQ
OC1A
(PB1)
T/C1 COMPARE
MATCH A IRQ
T/C CONTROL
REGISTER 1 (TCCR1)
COM1B1
PWM1A
PWM1B
COM1B0
FOC1A
FOC1B
(OCR1A)
(OCR1B)
(OCR1C)
8-BIT COMPARATOR
T/C1 OUTPUT
COMPARE REGISTER
TOV0
COM1A1
COM1A0
8-BIT COMPARATOR
T/C1 OUTPUT
COMPARE REGISTER
GLOBAL T/C CONTROL
REGISTER (GTCCR)
CS12
PSR1
CS11
CS10
CS13
CTC1
OC1A
(PB0)
OC1B
(PB4)
OC1B
(PB3)
DEAD TIME GENERATOR
DEAD TIME GENERATOR