Техническая Спецификация для Atmel ATmega328P Xplained Mini MEGA328P-XMINI MEGA328P-XMINI
Модели
MEGA328P-XMINI
121
ATmega48A/PA/88A/PA/168A/PA/328/P [DATASHEET]
Atmel-8271H-AVR- ATmega-Datasheet_08/2014
Figure 16-4.
Output Compare Unit, Block Diagram
The OCR1x Register is double buffered when using any of the twelve Pulse Width Modulation (PWM) modes.
For the Normal and Clear Timer on Compare (CTC) modes of operation, the double buffering is disabled. The
double buffering synchronizes the update of the OCR1x Compare Register to either TOP or BOTTOM of the
counting sequence. The synchronization prevents the occurrence of odd-length, non-symmetrical PWM pulses,
thereby making the output glitch-free.
For the Normal and Clear Timer on Compare (CTC) modes of operation, the double buffering is disabled. The
double buffering synchronizes the update of the OCR1x Compare Register to either TOP or BOTTOM of the
counting sequence. The synchronization prevents the occurrence of odd-length, non-symmetrical PWM pulses,
thereby making the output glitch-free.
The OCR1x Register access may seem complex, but this is not case. When the double buffering is enabled, the
CPU has access to the OCR1x Buffer Register, and if double buffering is disabled the CPU will access the
OCR1x directly. The content of the OCR1x (Buffer or Compare) Register is only changed by a write operation
(the Timer/Counter does not update this register automatically as the TCNT1 and ICR1 Register). Therefore
OCR1x is not read via the high byte temporary register (TEMP). However, it is a good practice to read the low
byte first as when accessing other 16-bit registers. Writing the OCR1x Registers must be done via the TEMP
Register since the compare of all 16 bits is done continuously. The high byte (OCR1xH) has to be written first.
When the high byte I/O location is written by the CPU, the TEMP Register will be updated by the value written.
Then when the low byte (OCR1xL) is written to the lower eight bits, the high byte will be copied into the upper 8-
bits of either the OCR1x buffer or OCR1x Compare Register in the same system clock cycle.
CPU has access to the OCR1x Buffer Register, and if double buffering is disabled the CPU will access the
OCR1x directly. The content of the OCR1x (Buffer or Compare) Register is only changed by a write operation
(the Timer/Counter does not update this register automatically as the TCNT1 and ICR1 Register). Therefore
OCR1x is not read via the high byte temporary register (TEMP). However, it is a good practice to read the low
byte first as when accessing other 16-bit registers. Writing the OCR1x Registers must be done via the TEMP
Register since the compare of all 16 bits is done continuously. The high byte (OCR1xH) has to be written first.
When the high byte I/O location is written by the CPU, the TEMP Register will be updated by the value written.
Then when the low byte (OCR1xL) is written to the lower eight bits, the high byte will be copied into the upper 8-
bits of either the OCR1x buffer or OCR1x Compare Register in the same system clock cycle.
For more information of how to access the 16-bit registers refer to
16.7.1 Force Output Compare
In non-PWM Waveform Generation modes, the match output of the comparator can be forced by writing a one
to the Force Output Compare (FOC1x) bit. Forcing compare match will not set the OCF1x Flag or reload/clear
the timer, but the OC1x pin will be updated as if a real compare match had occurred (the COM11:0 bits settings
define whether the OC1x pin is set, cleared or toggled).
to the Force Output Compare (FOC1x) bit. Forcing compare match will not set the OCF1x Flag or reload/clear
the timer, but the OC1x pin will be updated as if a real compare match had occurred (the COM11:0 bits settings
define whether the OC1x pin is set, cleared or toggled).
16.7.2 Compare Match Blocking by TCNT1 Write
All CPU writes to the TCNT1 Register will block any compare match that occurs in the next timer clock cycle,
even when the timer is stopped. This feature allows OCR1x to be initialized to the same value as TCNT1 without
triggering an interrupt when the Timer/Counter clock is enabled.
even when the timer is stopped. This feature allows OCR1x to be initialized to the same value as TCNT1 without
triggering an interrupt when the Timer/Counter clock is enabled.
OCFnx (Int.Req.)
=
(16-bit Comparator )
OCRnx Buffer (16-bit Register)
OCRnxH Buf. (8-bit)
OCnx
TEMP (8-bit)
DATA BUS
(8-bit)
OCRnxL Buf. (8-bit)
TCNTn (16-bit Counter)
TCNTnH (8-bit)
TCNTnL (8-bit)
COMnx1:0
WGMn3:0
OCRnx (16-bit Register)
OCRnxH (8-bit)
OCRnxL (8-bit)
Waveform Generator
TOP
BOTTOM