Manual
35
AT90S/LS8535
1041H–11/01
16-bit Timer/Counter1 Figure 31 shows the block diagram for Timer/Counter1.
Figure 31. Timer/Counter1 Block Diagram
The 16-bit Timer/Counter1 can select clock source from CK, prescaled CK or an exter-
nal pin. In addition, it can be stopped as described in the specification for the
Timer/Counter1 Control Registers (TCCR1A and TCCR1B). The different status flags
(Overflow, Compare Match and Capture Event) and control signals are found in the
Timer/Counter1 Control Registers (TCCR1A and TCCR1B). The interrupt enable/dis-
able settings for Timer/Counter1 are found in the Timer/Counter Interrupt Mask Register
(TIMSK).
When Timer/Counter1 is externally clocked, the external signal is synchronized with the
oscillator frequency of the CPU. To assure proper sampling of the external clock, the
minimum time between two external clock transitions must be at least one internal CPU
clock period. The external clock signal is sampled on the rising edge of the internal CPU
clock.
The 16-bit Timer/Counter1 features both a high-resolution and a high-accuracy usage
with the lower prescaling opportunities. Similarly, the high prescaling opportunities
makes the Timer/Counter1 useful for lower speed functions or exact timing functions
with infrequent actions.
The Timer/Counter1 supports two Output Compare functions using the Output Compare
Register 1A and B (OCR1A and OCR1B) as the data sources to be compared to the
Timer/Counter1 contents. The Output Compare functions include optional clearing of
8-BIT DA
TA BUS
T/C1 CONTROL
REGISTER B (TCCR1B)
T/C1 CONTROL
REGISTER A (TCCR1A)
T/C1 INPUT CAPTURE REGISTER (ICR1)
16 BIT COMPARATOR
16 BIT COMPARATOR
TIMER/COUNTER1 OUTPUT COMPARE REGISTER A
TIMER/COUNTER1 OUTPUT COMPARE REGISTER B
TIMER/COUNTER1 (TCNT1)
TIMER INT. FLAG
REGISTER (TIFR)
0
0
0
0
0
0
7
7
7
7
7
7
8
8
8
8
8
8
15
15
15
15
15
15
CONTROL
LOGIC
COM1A1
COM1B1
CS12
TOV1
TOV1
TOV0
OCF1A
OCF1A
OCF1B
OCF1B
ICF1
ICF1
COM1A0
COM1B0
CS11
CTC1
PWM11
PWM10
ICES1
ICNC1
CS10
C
K
T/C1 COMPARE
MATCHA IRQ
T/C1 COMPARE
MATCHB IRQ
T/C1 INPUT
CAPTURE IRQ
T/C1 OVER-
FLOW IRQ
CAPTURE
TRIGGER
T/C CLOCK SOURCE
T/C CLEAR
UP/DOWN
TIMER INT. MASK
REGISTER (TIMSK)
TOIE0
TOIE1
OCIE1A
OCIE1B
TICIE1
TOIE2
TOV2
OCIE2
OCF2
T1