atmega32u4-16mu ATMEL Corporation, atmega32u4-16mu Datasheet - Page 165

• Manufacturer Part Number: atmega32u4-16mu
• Description: Atmega32u4 8-bit Avr Microcontroller With 32k Bytes Of Isp Flash And Usb Controller
• Manufacturer: ATMEL Corporation

16.6
7766A–AVR–03/08
Compare Match Output Unit
The length of the counting period is user adjustable by selecting the dead time prescaler setting
by using the DTPS41:40 control bits, and selecting then the dead time value in I/O register DT4.
The DT4 register consists of two 4-bit fields, DT4H and DT4L that control the dead time periods
of the PWM output and its' complementary output separately in terms of the number of pres-
caled dead time generator clock cycles. Thus the rising edge of OC4x and OC4x can have
different dead time periods as the t
t
Figure 16-8. The Complementary Output Pair, COM4x1:0 = 1
The Compare Output Mode (COM4x1:0) bits have two functions. The Waveform Generator uses
the COM4x1:0 bits for defining the inverted or non-inverted Waveform Output (OCW4x) at the
next Compare Match. Also, the COM4x1:0 bits control the OC4x and OC4x pin output source.
Figure 16-9
I/O Registers, I/O bits, and I/O pins in the figure are shown in bold. Only the parts of the general
I/O Port Control Registers (DDR and PORT) that are affected by the COM4x1:0 bits are shown.
In Normal Mode (non-PWM) the Dead Time Generator is disabled and it is working like a syn-
chronizer: the Output Compare (OC4x) is delayed from the Waveform Output (OCW4x) by one
timer clock cycle. Whereas in Fast PWM Mode and in Phase and Frequency Correct PWM
Mode when the COM4x1:0 bits are set to “01” both the non-inverted and the inverted Output
Compare output are generated, and an user programmable Dead Time delay is inserted for
these complementary output pairs (OC4x and OC4x). The functionality in PWM modes is similar
to Normal mode when any other COM4x1:0 bit setup is used. When referring to the OC4x state,
the reference is for the Output Compare output (OC4x) from the Dead Time Generator, not the
OC4x pin. If a system reset occur, the OC4x is reset to “0”.
The general I/O port function is overridden by the Output Compare (OC4x / OC4x) from the
Dead Time Generator if either of the COM4x1:0 bits are set. However, the OC4x pin direction
(input or output) is still controlled by the Data Direction Register (DDR) for the port pin. The Data
Direction Register bit for the OC4x and OC4x pins (DDR_OC4x and DDR_OC4x) must be set as
output before the OC4x and OC4x values are visible on the pin. The port override function is
independent of the Output Compare mode.
The design of the Output Compare Pin Configuration logic allows initialization of the OC4x state
before the output is enabled. Note that some COM4x1:0 bit settings are reserved for certain
modes of operation. For Output Compare Pin Configurations refer to
Table 16-3 on page
OCWnx
OCnx
OCnx
(COMnx = 1)
non-overlap / falling edge
t
non-overlap / rising edge
shows a simplified schematic of the logic affected by the COM4x1:0 bit setting. The
is adjusted by the 4-bit DT4L value.
171,
Table 16-4 on page
t
non-overlap / falling edge
non-overlap / rising edge
173, and
is adjusted by the 4-bit DT4H value and the
Table 16-5 on page
ATmega32U4
Table 16-2 on page
174.
170,
165