ATMEGA325A-MU Atmel, ATMEGA325A-MU Datasheet - Page 148

• Manufacturer Part Number: ATMEGA325A-MU
• Description: IC MCU AVR 32K FLASH 64VQFN
• Manufacturer: Atmel
• Series: AVR® ATmegar

Specifications of ATMEGA325A-MU

• Core Processor: AVR
• Core Size: 8-Bit
• Speed: 20MHz
• Connectivity: SPI, UART/USART, USI
• Peripherals: Brown-out Detect/Reset, POR, PWM, WDT
• Number Of I /o: 54
• Program Memory Size: 32KB (16K x 16)
• Program Memory Type: FLASH
• Eeprom Size: 1K x 8
• Ram Size: 2K x 8
• Voltage - Supply (vcc/vdd): 1.8 V ~ 5.5 V
• Data Converters: A/D 8x10b
• Oscillator Type: Internal
• Operating Temperature: -40°C ~ 85°C
• Package / Case: 64-VFQFN Exposed Pad
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

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ATmega165A/165PA/325A/325PA/3250A/3250PA/645A/645P/645
The counter counts repeatedly from BOTTOM to MAX and then from MAX to BOTTOM. In non-
inverting Compare Output mode, the Output Compare (OC2A) is cleared on the compare match
between TCNT2 and OCR2A while upcounting, 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 sym-
metric 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 TCNT2 value will be equal to MAX for one
timer clock cycle. The timing diagram for the phase correct PWM mode is shown on
The TCNT2 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 TCNT2 slopes represent compare matches between OCR2A and TCNT2.
Figure 17-7. Phase Correct PWM Mode, Timing Diagram
The Timer/Counter Overflow Flag (TOV2) is set each time the counter reaches BOTTOM. 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
OC2A pin. Setting the COM2A[1:0] bits to two will produce a non-inverted PWM. An inverted
PWM output can be generated by setting the COM2A[1:0] to three (See
155). The actual OC2A 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 OC2A Register
at the compare match between OCR2A and TCNT2 when the counter increments, and setting
(or clearing) the OC2A Register at compare match between OCR2A and TCNT2 when the coun-
ter decrements. The PWM frequency for the output when using phase correct PWM can be
calculated by the following equation:
TCNTn
OCnx
OCnx
Period
1
f
OCnxPCPWM
2
=
----------------- -
N 510
f
clk_I/O
⋅
3
OCnx Interrupt Flag Set
OCRnx Update
TOVn Interrupt Flag Set
(COMnx1:0 = 2)
(COMnx1:0 = 3)
Table 17-5 on page
8285B–AVR–03/11
Figure
17-7.