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