ATMEGA8535L-8AC Atmel, ATMEGA8535L-8AC Datasheet - Page 79

• Manufacturer Part Number: ATMEGA8535L-8AC
• Description: IC AVR MCU 8K LV 8MHZ COM 44TQFP
• Manufacturer: Atmel
• Series: AVR® ATmegar

Specifications of ATMEGA8535L-8AC

• Core Processor: AVR
• Core Size: 8-Bit
• Speed: 8MHz
• Connectivity: I²C, SPI, UART/USART
• Peripherals: Brown-out Detect/Reset, POR, PWM, WDT
• Number Of I /o: 32
• Program Memory Size: 8KB (4K x 16)
• Program Memory Type: FLASH
• Eeprom Size: 512 x 8
• Ram Size: 512 x 8
• Voltage - Supply (vcc/vdd): 2.7 V ~ 5.5 V
• Data Converters: A/D 8x10b
• Oscillator Type: Internal
• Operating Temperature: 0°C ~ 70°C
• Package / Case: 44-TQFP, 44-VQFP
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

Phase Correct PWM Mode
2502K–AVR–10/06
The phase correct PWM mode (WGM01:0 = 1) provides a high resolution phase correct
PWM waveform generation option. The phase correct PWM mode is based on a dual-
slope operation. The counter counts repeatedly from BOTTOM to MAX and then from
MAX to BOTTOM. In non-inverting Compare Output mode, the Output Compare (OC0)
is cleared on the Compare Match between TCNT0 and OCR0 while up-counting, and
set on the Compare Match while down-counting. In inverting Output Compare mode, the
operation is inverted. The dual-slope operation has lower maximum operation frequency
than single slope operation. However, due to the symmetric feature of the dual-slope
PWM modes, these modes are preferred for motor control applications.
The PWM resolution for the phase correct PWM mode is fixed to eight bits. In phase
correct PWM mode the counter is incremented until the counter value matches MAX.
When the counter reaches MAX, it changes the count direction. The TCNT0 value will
be equal to MAX for one timer clock cycle. The timing diagram for the phase correct
PWM mode is shown on Figure 33. The TCNT0 value is in the timing diagram shown as
a histogram for illustrating the dual-slope operation. The diagram includes non-inverted
and inverted PWM outputs. The small horizontal line marks on the TCNT0 slopes repre-
sent compare matches between OCR0 and TCNT0.
Figure 33. Phase Correct PWM Mode, Timing Diagram
The Timer/Counter Overflow Flag (TOV0) is set each time the counter reaches BOT-
TOM. The interrupt flag can be used to generate an interrupt each time the counter
reaches the BOTTOM value.
In phase correct PWM mode, the compare unit allows generation of PWM waveforms on
the OC0 pin. Setting the COM01:0 bits to two will produce a non-inverted PWM. An
inverted PWM output can be generated by setting the COM01:0 to three (See Table 42
on page 84). The actual OC0 value will only be visible on the port pin if the data direction
for the port pin is set as output. The PWM waveform is generated by clearing (or setting)
the OC0 Register at the Compare Match between OCR0 and TCNT0 when the counter
increments, and setting (or clearing) the OC0 Register at Compare Match between
TCNTn
Period
OCn
OCn
1
2
ATmega8535(L)
3
OCn Interrupt Flag Set
OCRn Update
TOVn Interrupt Flag Set
(COMn1:0 = 2)
(COMn1:0 = 3)
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