Datasheet
109
ATtiny828 [DATASHEET]
8371A–AVR–08/12
synchronization prevents the occurrence of odd-length, non-symmetrical PWM pulses, thereby making the output glitch-
free.
Figure 40. Output Compare Unit, Block Diagram
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.
For more information of how to access the 16-bit registers refer to “Accessing 16-bit Registers” on page 120.
12.6.1 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 (1x) 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 COM1[1:0] bits settings define whether the OC1x
pin is set, cleared or toggled).
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)
COMnx[1:0]WGMn[3:0]
OCRnx (16-bit Register)
OCRnxH (8-bit) OCRnxL (8-bit)
Waveform Generator
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