ATTINY861A-SU Atmel, ATTINY861A-SU Datasheet - Page 76

• Manufacturer Part Number: ATTINY861A-SU
• Description: IC, MCU, 8BIT, 8K FLASH, 20SOIC
• Manufacturer: Atmel

Specifications of ATTINY861A-SU

• Controller Family/series: ATtiny
• No. Of I/o's: 16
• Eeprom Memory Size: 512Byte
• Ram Memory Size: 512Byte
• Cpu Speed: 20MHz
• No.: RoHS Compliant
• Core Size: 8bit
• Program Memory Size: 8KB
• Oscillator Type: External, Internal
• Rohs Compliant: Yes

11.7.2
11.7.3
76
ATtiny261A/461A/861A
Clear Timer on Compare Match (CTC) 8-bit Mode
Normal, 16-bit Mode
The Overflow Flag (TOV0) is set in the same timer clock cycle as when TCNT0L becomes zero.
The TOV0 Flag in this case behaves like a ninth bit, except that it is only set, not cleared. How-
ever, combined with the timer overflow interrupt that automatically clears the TOV0 Flag, the
timer resolution can be increased by software. There are no special cases to consider in the
Normal 8-bit mode, a new counter value can be written anytime. The Output Compare Unit can
be used to generate interrupts at some given time.
In Clear Timer on Compare or CTC mode, see
used to manipulate the counter resolution. In CTC mode the counter is cleared to zero when the
counter value (TCNT0) matches the OCR0A. The OCR0A defines the top value for the counter,
hence also its resolution. This mode allows greater control of the Compare Match output fre-
quency. It also simplifies the operation of counting external events.
The timing diagram for the CTC mode is shown in
increases until a Compare Match occurs between TCNT0 and OCR0A, and then counter
(TCNT0) is cleared.
Figure 11-6. CTC Mode, Timing Diagram
An interrupt can be generated each time the counter value reaches the TOP value by using the
OCF0A Flag. If the interrupt is enabled, the interrupt handler routine can be used for updating
the TOP value. However, changing TOP to a value close to BOTTOM when the counter is run-
ning with none or a low prescaler value must be done with care since the CTC mode does not
have the double buffering feature. If the new value written to OCR0A is lower than the current
value of TCNT0, the counter will miss the Compare Match. The counter will then have to count to
its maximum value (0xFF) and wrap around starting at 0x00 before the Compare Match can
occur. As for the Normal mode of operation, the TOV0 Flag is set in the same timer clock cycle
that the counter counts from MAX to 0x00.
In 16-bit mode, see
overruns when it passes its maximum 16-bit value (MAX = 0xFFFF) and then restarts from the
bottom (0x0000). The Overflow Flag (TOV0) will be set in the same timer clock cycle as the
TCNT0H/L becomes zero. The TOV0 Flag in this case behaves like a 17th bit, except that it is
only set, not cleared. However, combined with the timer overflow interrupt that automatically
clears the TOV0 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 Output
Compare Unit can be used to generate interrupts at some given time.
TCNTn
Period
1
Table 11-3 on page
2
75, the counter (TCNT0H/L) is a incrementing until it
3
Table 11-3 on page
Figure
4
11-6. The counter value (TCNT0)
75, the OCR0A Register is
OCnx Interrupt Flag Set
8197B–AVR–01/10