AT90LS4433-4AI datasheet(36/126 Pages) ATMEL

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AT90S/LS4433

1042H–AVR–04/03

Interrupt Flag Register (TIFR). The interrupt enable/disable settings for Timer/Counter1

are found in the Timer/Counter Interrupt Mask Register (TIMSK).

When Timer/Counter1 is externally clocked, the external signal is synchronized with the

Oscillator frequency of the CPU. To assure proper sampling of the external clock, the

minimum time between two external clock transitions must be at least one internal CPU

clock period. The external clock signal is sampled on the rising edge of the internal CPU

clock.

The 16-bit Timer/Counter1 features both a high resolution and a high-accuracy usage

with the lower prescaling opportunities. Similarly, the high prescaling opportunities

makes the Timer/Counter1 useful for lower speed functions or exact timing functions

with infrequent actions.

The Timer/Counter1 supports an Output Compare function using the Output Compare

Register1 (OCR1) as the data source to be compared to the Timer/Counter1 contents.

The Output Compare functions include optional clearing of the counter on compare

matches and actions on the Output Compare pin 1 on compare matches.

Timer/Counter1 can also be used as a 8-, 9-, or 10-bit Pulse Width Modulator. In this

mode, the counter and the OCR1 Register serve as a glitch-free, stand-alone PWM with

centered pulses. Refer to page 41 for a detailed description of this function.

The Input Capture function of Timer/Counter1 provides a capture of the Timer/Counter1

contents to the Input Capture Register (ICR1), triggered by an external event on the

Input Capture Pin (ICP). The actual capture event settings are defined by the

Timer/Counter1 Control Register (TCCR1). In addition, the Analog Comparator can be

set to trigger the Input Capture. Refer to the section, “The Analog Comparator”, for

details of this. The ICP pin logic is shown in Figure 33.

Figure 33. ICP Pin Schematic Diagram

If the Noise Canceler function is enabled, the actual trigger condition for the capture

event is monitored over four samples, and all four must be equal to activate the Capture

Flag. The input pin signal is sampled at XTAL clock frequency.

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