ATmega640 Atmel Corporation, ATmega640 Datasheet - Page 150
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ATmega640
Manufacturer Part Number
ATmega640
Description
Manufacturer
Atmel Corporation
Specifications of ATmega640
Flash (kbytes)
64 Kbytes
Pin Count
100
Max. Operating Frequency
16 MHz
Cpu
8-bit AVR
# Of Touch Channels
16
Hardware Qtouch Acquisition
No
Max I/o Pins
86
Ext Interrupts
32
Usb Speed
No
Usb Interface
No
Spi
5
Twi (i2c)
1
Uart
4
Graphic Lcd
No
Video Decoder
No
Camera Interface
No
Adc Channels
16
Adc Resolution (bits)
10
Adc Speed (ksps)
15
Analog Comparators
1
Resistive Touch Screen
No
Temp. Sensor
No
Crypto Engine
No
Sram (kbytes)
8
Eeprom (bytes)
4096
Self Program Memory
YES
Dram Memory
No
Nand Interface
No
Picopower
No
Temp. Range (deg C)
-40 to 85
I/o Supply Class
1.8 to 5.5
Operating Voltage (vcc)
1.8 to 5.5
Fpu
No
Mpu / Mmu
no / no
Timers
6
Output Compare Channels
16
Input Capture Channels
4
Pwm Channels
15
32khz Rtc
Yes
Calibrated Rc Oscillator
Yes
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Quantity
Price
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17.9.3
2549N–AVR–05/11
Fast PWM Mode
TCNTn, the counter will miss the compare match. The counter will then have to count to its max-
imum value (0xFFFF) and wrap around starting at 0x0000 before the compare match can occur.
In many cases this feature is not desirable. An alternative will then be to use the fast PWM mode
using OCRnA for defining TOP (WGMn3:0 = 15) since the OCRnA then will be double buffered.
For generating a waveform output in CTC mode, the OCnA output can be set to toggle its logical
level on each compare match by setting the Compare Output mode bits to toggle mode
(COMnA1:0 = 1). The OCnA value will not be visible on the port pin unless the data direction for
the pin is set to output (DDR_OCnA = 1). The waveform generated will have a maximum fre-
quency of f
defined by the following equation:
The N variable represents the prescaler factor (1, 8, 64, 256, or 1024).
As for the Normal mode of operation, the TOVn Flag is set in the same timer clock cycle that the
counter counts from MAX to 0x0000.
The fast Pulse Width Modulation or fast PWM mode (WGMn3:0 = 5, 6, 7, 14, or 15) provides a
high frequency PWM waveform generation option. The fast PWM differs from the other PWM
options by its single-slope operation. The counter counts from BOTTOM to TOP then restarts
from BOTTOM. In non-inverting Compare Output mode, the Output Compare (OCnx) is cleared
on the compare match between TCNTn and OCRnx, and set at BOTTOM. In inverting Compare
Output mode output is set on compare match and cleared at BOTTOM. Due to the single-slope
operation, the operating frequency of the fast PWM mode can be twice as high as the phase cor-
rect and phase and frequency correct PWM modes that use dual-slope operation. This high
frequency makes the fast PWM mode well suited for power regulation, rectification, and DAC
applications. High frequency allows physically small sized external components (coils, capaci-
tors), hence reduces total system cost.
The PWM resolution for fast PWM can be fixed to 8-bit, 9-bit, or 10-bit, or defined by either ICRn
or OCRnA. The minimum resolution allowed is 2-bit (ICRn or OCRnA set to 0x0003), and the
maximum resolution is 16-bit (ICRn or OCRnA set to MAX). The PWM resolution in bits can be
calculated by using the following equation:
In fast PWM mode the counter is incremented until the counter value matches either one of the
fixed values 0x00FF, 0x01FF, or 0x03FF (WGMn3:0 = 5, 6, or 7), the value in ICRn (WGMn3:0 =
14), or the value in OCRnA (WGMn3:0 = 15). The counter is then cleared at the following timer
clock cycle. The timing diagram for the fast PWM mode is shown in
The figure shows fast PWM mode when OCRnA or ICRn is used to define TOP. The TCNTn
value is in the timing diagram shown as a histogram for illustrating the single-slope operation.
The diagram includes non-inverted and inverted PWM outputs. The small horizontal line marks
on the TCNTn slopes represent compare matches between OCRnx and TCNTn. The OCnx
Interrupt Flag will be set when a compare match occurs.
OC
n
A
= f
clk_I/O
/2 when OCRnA is set to zero (0x0000). The waveform frequency is
ATmega640/1280/1281/2560/2561
f
OCnA
R
FPWM
=
-------------------------------------------------- -
2 N
=
⋅
log
---------------------------------- -
⋅
(
f
(
1
clk_I/O
log
TOP
+
2 ( )
OCRnA
+
1
)
)
Figure 17-7 on page
151.
150
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