attiny167-esxz ATMEL Corporation, attiny167-esxz Datasheet - Page 123

• Manufacturer Part Number: attiny167-esxz
• Description: 8-bit Avr 8-bit Microcontroller Microcontroller With 16k Bytes In-system Programmable Flash And Lin Controller
• Manufacturer: ATMEL Corporation

7728A–AUTO–07/08
Figure 12-10. Phase and Frequency Correct PWM Mode, Timing Diagram
The Timer/Counter Overflow Flag (TOV1) is set at the same timer clock cycle as the OCR1A/B
Registers are updated with the double buffer value (at BOTTOM). When either OCR1A or ICR1
is used for defining the TOP value, the OC1A or ICF1 flag set when TCNT1 has reached TOP.
The interrupt flags can then be used to generate an interrupt each time the counter reaches the
TOP or BOTTOM value.
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 TCNT1 and the OCR1A/B.
As
rical in all periods. Since the OCR1A/B Registers are updated at BOTTOM, the length of the
rising and the falling slopes will always be equal. This gives symmetrical output pulses and is
therefore frequency correct.
Using the ICR1 Register for defining TOP works well when using fixed TOP values. By using
ICR1, the OCR1A Register is free to be used for generating a PWM output on OC1A. However,
if the base PWM frequency is actively changed by changing the TOP value, using the OCR1A as
TOP is clearly a better choice due to its double buffer feature.
In phase and frequency correct PWM mode, the compare units allow generation of PWM wave-
forms on the OC1A/B pins. Setting the COM1A/B1:0 bits to two will produce a non-inverted
PWM and an inverted PWM output can be generated by setting the COM1A/B1:0 to three (See
Table on page
direction for the port pin is set as output (DDR_OC1A/B) and OC1A/Bi is set. The PWM wave-
form is generated by setting (or clearing) the OC1A/B Register at the compare match between
OCR1A/B and TCNT1 when the counter increments, and clearing (or setting) the OC1A/B Reg-
ister at compare match between OCR1A/B and TCNT1 when the counter decrements. The
PWM frequency for the output when using phase and frequency correct PWM can be calculated
by the following equation:
Figure 12-10
OCnxi
OCnxi
TCNTn
Period
126). The actual OC1A/B value will only be visible on the port pin if the data
shows the output generated is, in contrast to the phase correct mode, symmet-
1
f
OCnxPFCPWM
2
=
3
--------------------------- -
2 N TOP
⋅
f
clk_I/O
⋅
4
OCnA Interrupt Flag Set
or ICFn Interrupt Flag Set
(Interrupt on TOP)
(COMnx1:0 = 2)
(COMnx1:0 = 3)
OCRnx/TOP Update and
TOVn Interrupt Flag Set
(Interrupt on Bottom)
ATtiny167
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