(OC1A/B). See “Output Compare Units” on page 94. The compare match event will also
set the Compare Match Flag (OCF1A/B) which can be used to generate an output com-
pare interrupt request.
The Input Capture Register can capture the Timer/Counter value at a given external
(edge triggered) event on either the Input Capture Pin (ICP1) or on the Analog Compar-
ator pins (See “Analog Comparator” on page 198.) The Input Capture unit includes a
digital filtering unit (Noise Canceler) for reducing the chance of capturing noise spikes.
The TOP value, or maximum Timer/Counter value, can in some modes of operation be
defined by either the OCR1A Register, the ICR1 Register, or by a set of fixed values.
When using OCR1A as TOP value in a PWM mode, the OCR1A Register can not be
used for generating a PWM output. However, the TOP value will in this case be double
buffered allowing the TOP value to be changed in run time. If a fixed TOP value is
required, the ICR1 Register can be used as an alternative, freeing the OCR1A to be
used as PWM output.
Definitions
The following definitions are used extensively throughout the document:
Table 43. Definitions
BOTTOM
The counter reaches the BOTTOM when it becomes 0x0000.
MAX
The counter reaches its MAXimum when it becomes 0xFFFF (decimal 65535).
The counter reaches the TOP when it becomes equal to the highest value in the
count sequence. The TOP value can be assigned to be one of the fixed values:
0x00FF, 0x01FF, or 0x03FF, or to the value stored in the OCR1A or ICR1 Regis-
ter. The assignment is dependent of the mode of operation.
TOP
Compatibility
The 16-bit Timer/Counter has been updated and improved from previous versions of the
16-bit AVR Timer/Counter. This 16-bit Timer/Counter is fully compatible with the earlier
version regarding:
•
•
•
All 16-bit Timer/Counter related I/O Register address locations, including Timer
Interrupt Registers.
Bit locations inside all 16-bit Timer/Counter Registers, including Timer Interrupt
Registers.
Interrupt Vectors.
The following control bits have changed name, but have same functionality and register
location:
•
•
•
PWM10 is changed to WGM10.
PWM11 is changed to WGM11.
CTC1 is changed to WGM12.
The following bits are added to the 16-bit Timer/Counter Control Registers:
•
•
FOC1A and FOC1B are added to TCCR1A.
WGM13 is added to TCCR1B.
The 16-bit Timer/Counter has improvements that will affect the compatibility in some
special cases.
88
ATmega32(L)
2503J–AVR–10/06
ATMEL [ ATMEL ]
