ATmega88PA Automotive Atmel Corporation, ATmega88PA Automotive Datasheet - Page 120

• Manufacturer Part Number: ATmega88PA Automotive
• Manufacturer: Atmel Corporation

16.7
120
Output Compare Units
Atmel ATmega48PA/88PA/168PA [Preliminary]
Measurement of an external signal’s duty cycle requires that the trigger edge is changed after
each capture. Changing the edge sensing must be done as early as possible after the ICR1
Register has been read. After a change of the edge, the Input Capture Flag (ICF1) must be
cleared by software (writing a logical one to the I/O bit location). For measuring frequency
only, the clearing of the ICF1 Flag is not required (if an interrupt handler is used).
The 16-bit comparator continuously compares TCNT1 with the Output Compare Register
(OCR1x). If TCNT equals OCR1x the comparator signals a match. A match will set the Output
Compare Flag (OCF1x) at the next timer clock cycle. If enabled (OCIE1x = 1), the Output
Compare Flag generates an Output Compare interrupt. The OCF1x Flag is automatically
cleared when the interrupt is executed. Alternatively the OCF1x Flag can be cleared by soft-
ware by writing a logical one to its I/O bit location. The Waveform Generator uses the match
signal to generate an output according to operating mode set by the Waveform Generation
mode (WGM13:0) bits and Compare Output mode (COM1x1:0) bits. The TOP and BOTTOM
signals are used by the Waveform Generator for handling the special cases of the extreme
values in some modes of operation
A special feature of Output Compare unit A allows it to define the Timer/Counter TOP value
(i.e., counter resolution). In addition to the counter resolution, the TOP value defines the
period time for waveforms generated by the Waveform Generator.
Figure 16-4
and bit names indicates the device number (n = 1 for Timer/Counter 1), and the “x” indicates
Output Compare unit (A/B). The elements of the block diagram that are not directly a part of
the Output Compare unit are gray shaded.
Figure 16-4. Output Compare Unit, Block Diagram
shows a block diagram of the Output Compare unit. The small “n” in the register
OCRnxH Buf. (8-bit)
OCRnxH (8-bit)
BOTTOM
OCRnx Buffer (16-bit Register)
TEMP (8-bit)
TOP
OCRnx (16-bit Register)
(See “Modes of Operation” on page
OCRnxL Buf. (8-bit)
OCRnxL (8-bit)
DATA BUS
Waveform Generator
WGMn3:0
=
(16-bit Comparator )
(8-bit)
COMnx1:0
TCNTnH (8-bit)
OCFnx (Int.Req.)
TCNTn (16-bit Counter)
123.)
TCNTnL (8-bit)
9223B–AVR–09/11
OCnx