ATMEGA8A-AUR Atmel, ATMEGA8A-AUR Datasheet - Page 95
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ATMEGA8A-AUR
Manufacturer Part Number
ATMEGA8A-AUR
Description
MCU AVR 8KB FLASH 16MHZ 32TQFP
Manufacturer
Atmel
Series
AVR® ATmegar
Datasheet
1.ATMEGA8A-MU.pdf
(308 pages)
Specifications of ATMEGA8A-AUR
Core Processor
AVR
Core Size
8-Bit
Speed
16MHz
Connectivity
I²C, SPI, UART/USART
Peripherals
Brown-out Detect/Reset, POR, PWM, WDT
Number Of I /o
23
Program Memory Size
8KB (4K x 16)
Program Memory Type
FLASH
Eeprom Size
512 x 8
Ram Size
1K x 8
Voltage - Supply (vcc/vdd)
2.7 V ~ 5.5 V
Data Converters
A/D 8x10b
Oscillator Type
Internal
Operating Temperature
-40°C ~ 85°C
Package / Case
*
Lead Free Status / RoHS Status
Lead free / RoHS Compliant
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Part Number
Manufacturer
Quantity
Price
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16.9.5
8159D–AVR–02/11
Phase and Frequency Correct PWM Mode
two slopes of the period will differ in length. The difference in length gives the unsymmetrical
result on the output.
It is recommended to use the Phase and Frequency Correct mode instead of the Phase Correct
mode when changing the TOP value while the Timer/Counter is running. When using a static
TOP value there are practically no differences between the two modes of operation.
In phase correct PWM mode, the compare units allow generation of PWM waveforms on the
OC1x pins. Setting the COM1x1:0 bits to 2 will produce a non-inverted PWM and an inverted
PWM output can be generated by setting the COM1x1:0 to 3. See
actual OC1x value will only be visible on the port pin if the data direction for the port pin is set as
output (DDR_OC1x). The PWM waveform is generated by setting (or clearing) the OC1x Regis-
ter at the Compare Match between OCR1x and TCNT1 when the counter increments, and
clearing (or setting) the OC1x Register at Compare Match between OCR1x and TCNT1 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 prescaler divider (1, 8, 64, 256, or 1024).
The extreme values for the OCR1x Register represent special cases when generating a PWM
waveform output in the phase correct PWM mode. If the OCR1x is set equal to BOTTOM the
output will be continuously low and if set equal to TOP the output will be continuously high for
non-inverted PWM mode. For inverted PWM the output will have the opposite logic values.
If OCR1A is used to define the TOP value (WMG13:0 = 11) and COM1A1:0 = 1, the OC1A out-
put will toggle with a 50% duty cycle.
The phase and frequency correct Pulse Width Modulation, or phase and frequency correct PWM
mode (WGM13:0 = 8 or 9) provides a high resolution phase and frequency correct PWM wave-
form generation option. The phase and frequency correct PWM mode is, like the phase correct
PWM mode, based on a dual-slope operation. The counter counts repeatedly from BOTTOM
(0x0000) to TOP and then from TOP to BOTTOM. In non-inverting Compare Output mode, the
Output Compare (OC1x) is cleared on the Compare Match between TCNT1 and OCR1x while
upcounting, and set on the Compare Match while downcounting. In inverting Compare Output
mode, the operation is inverted. The dual-slope operation gives a lower maximum operation fre-
quency compared to the single-slope operation. However, due to the symmetric feature of the
dual-slope PWM modes, these modes are preferred for motor control applications.
The main difference between the phase correct, and the phase and frequency correct PWM
mode is the time the OCR1x Register is updated by the OCR1x Buffer Register, (see
8
The PWM resolution for the phase and frequency correct PWM mode can be defined by either
ICR1 or OCR1A. The minimum resolution allowed is 2-bit (ICR1 or OCR1A set to 0x0003), and
the maximum resolution is 16-bit (ICR1 or OCR1A set to MAX). The PWM resolution in bits can
be calculated using the following equation:
In phase and frequency correct PWM mode the counter is incremented until the counter value
matches either the value in ICR1 (WGM13:0 = 8), or the value in OCR1A (WGM13:0 = 9). The
and
Figure
16-9).
R
f
OCnxPCPWM
PFCPWM
=
log
---------------------------------- -
=
--------------------------- -
2 N TOP
(
log
TOP
⋅
f
clk_I/O
2 ( )
⋅
+
1
)
Table 16-4 on page
ATmega8A
Figure 16-
100. The
95
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