atmega32c1 ATMEL Corporation, atmega32c1 Datasheet - Page 98

• Manufacturer Part Number: atmega32c1
• Description: Atmega32m1 Automotive 8-bit Avr Microcontroller With 32k/64k Bytes In-system Programmable Flash
• Manufacturer: ATMEL Corporation

12.7
98
Timer/Counter Timing Diagrams
ATmega32/64/M1/C1
match between OCR0x and TCNT0 when the counter decrements. The PWM frequency for the
output when using phase correct PWM can be calculated by the following equation:
The N variable represents the prescale factor (1, 8, 64, 256, or 1024).
The extreme values for the OCR0A Register represent special cases when generating a PWM
waveform output in the phase correct PWM mode. If the OCR0A is set equal to BOTTOM, the
output will be continuously low and if set equal to MAX the output will be continuously high for
non-inverted PWM mode. For inverted PWM the output will have the opposite logic values.
At the very start of period 2 in
there is no Compare Match. The point of this transition is to guarantee symmetry around BOT-
TOM. There are two cases that give a transition without Compare Match.
•
•
The Timer/Counter is a synchronous design and the timer clock (clk
clock enable signal in the following figures. The figures include information on when interrupt
flags are set.
shows the count sequence close to the MAX value in all modes other than phase correct PWM
mode.
Figure 12-8. Timer/Counter Timing Diagram, no Prescaling
Figure 12-9
OCRnx changes its value from MAX, like in
OCn pin value is the same as the result of a down-counting Compare Match. To ensure
symmetry around BOTTOM the OCnx value at MAX must correspond to the result of an up-
counting Compare Match.
The timer starts counting from a value higher than the one in OCRnx, and for that reason
misses the Compare Match and hence the OCnx change that would have happened on the
way up.
TCNTn
(clk
TOVn
clk
clk
I/O
I/O
Tn
/1)
shows the same timing data, but with the prescaler enabled.
Figure 12-8
MAX - 1
contains timing data for basic Timer/Counter operation. The figure
Figure 12-7
f
OCnxPCPWM
OCnx has a transition from high to low even though
MAX
Figure
=
----------------- -
N 510
f
clk_I/O
12-7. When the OCR0A value is MAX the
⋅
BOTTOM
T0
) is therefore shown as a
BOTTOM + 1
7647A–AVR–02/08