Rainbow Electronics ATtiny10 - Manual (Page 64)

64
8127B–AVR–08/09
ATtiny4/5/9/10
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-, 9-, or 10-bit, or defined by either ICR0 or
OCR0A. The minimum resolution allowed is 2-bit (ICR0 or OCR0A set to 0x0003), and the max-
imum resolution is 16-bit (ICR0 or OCR0A 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 (WGM03:0 = 5, 6, or 7), the value in ICR0 (WGM03:0 =
14), or the value in OCR0A (WGM03:0 = 15). The counter is then cleared at the following timer
clock cycle. The timing diagram for the fast PWM mode is shown in
Figure 11-9 on page 64 . The
figure shows fast PWM mode when OCR0A or ICR0 is used to define TOP. The TCNT0 value is
in the timing diagram shown as a histogram for illustrating the single-slope operation. The dia-
gram includes non-inverted and inverted PWM outputs. The small horizontal line marks on the
TCNT0 slopes represent compare matches between OCR0x and TCNT0. The OC0x interrupt
flag will be set when a compare match occurs.
Figure 11-9. Fast PWM Mode, Timing Diagram
The Timer/Counter Overflow Flag (TOV0) is set each time the counter reaches TOP. In addition
the OC0A or ICF0 flag is set at the same timer clock cycle as TOV0 is set when either OCR0A or
ICR0 is used for defining the TOP value. If one of the interrupts are enabled, the interrupt han-
dler routine can be used for updating the TOP and compare values.
When changing the TOP value the program must ensure that the new TOP value is higher or
equal to the value of all of the Compare Registers. If the TOP value is lower than any of the
Compare Registers, a compare match will never occur between the TCNT0 and the OCR0x.
Note that when using fixed TOP values the unused bits are masked to zero when any of the
OCR0x Registers are written.
R
FPWM
TOP 1 +
( )
log
2
( )
log
----------------------------------- =
TCNTn
OCRnx/TOP Update and
TOVn Interrupt Flag Set and
OCnA Interrupt Flag Set
or ICFn Interrupt Flag Set
(Interrupt on TOP)
1 7 Period 2 3 4 5 6 8
OCnx
OCnx
(COMnx1:0 = 2)
(COMnx1:0 = 3)