AT90CAN128-16AE ATMEL Corporation, AT90CAN128-16AE Datasheet - Page 119

• Manufacturer Part Number: AT90CAN128-16AE
• Description: 8-bit Avr Microcontroller With 128K Bytes of Isp Flash And CAN Controller.flash (Kbytes) 128 Vcc (V) 2.7-5.5 EEPROM (Kbytes) 4 SRAM (bytes) 4K CAN (mess. Obj.) 15
• Manufacturer: ATMEL Corporation

Output Compare Units
4250C–CAN–03/04
Using the Input Capture unit in any mode of operation when the TOP value (resolution)
is actively changed during operation, is not recommended.
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 ICRn Register has been read. After a change of the edge, the Input Capture Flag
(ICFn) must be cleared by software (writing a logical one to the I/O bit location). For
measuring frequency only, the clearing of the ICFn flag is not required (if an interrupt
handler is used).
The 16-bit comparator continuously compares TCNTn with the Output Compare Regis-
ter (OCRnx). If TCNT equals OCRnx the comparator signals a match. A match will set
the Output Compare Flag (OCFnx) at the next timer clock cycle. If enabled (OCIEnx =
1), the Output Compare Flag generates an Output Compare interrupt. The OCFnx flag is
automatically cleared when the interrupt is executed. Alternatively the OCFnx flag can
be cleared by software by writing a logical one to its I/O bit location. The Waveform Gen-
erator uses the match signal to generate an output according to operating mode set by
the Waveform Generation mode (WGMn3:0) bits and Compare O utput mode
(COMnx1:0) 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 (See
“Modes of Operation” on page 122 )
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 50 shows a block diagram of the Output Compare unit. The elements of the block
diagram that are not directly a part of the Output Compare unit are gray shaded.
Figure 50. Output Compare Unit, Block Diagram
OCRnxH Buf.(8-bit)
OCRnxH (8-bit)
BOTTOM
OCRnx Buffer (16-bit Register)
TEMP (8-bit)
TOP
OCRnx (16-bit Register)
OCRnxL Buf.(8-bit)
OCRnxL (8-bit)
DATA BUS
Waveform Generator
WGMn3:0
=
(16-bit Comparator )
(8-bit)
COMnx1:0
TCNTnH (8-bit)
OCFnx
AT90CAN128
TCNTn (16-bit Counter)
(Int.Req.)
TCNTnL (8-bit)
OCnx
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