AT90LS4433-4AI datasheet(38/126 Pages) ATMEL

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AT90S/LS4433

1042H–AVR–04/03

Timer/Counter1 Control

• Bit 7 – ICNC1: Input Capture1 Noise Canceler (4 CKs)

When the ICNC1 bit is cleared (zero), the Input Capture trigger Noise Canceler function

is disabled. The Input Capture is triggered at the first rising/falling edge sampled on the

ICP (Input Capture Pin) as specified. When the ICNC1 bit is set (one), four successive

samples are measured on the ICP (Input Capture Pin), and all samples must be

high/low according to the input capture trigger specification in the ICES1 bit. The actual

sampling frequency is the XTAL clock frequency.

• Bit 6 – ICES1: Input Capture1 Edge Select

While the ICES1 bit is cleared (zero), the Timer/Counter1 contents are transferred to the

Input Capture Register (ICR1) on the falling edge of the Input Capture Pin (ICP). While

the ICES1 bit is set (one), the Timer/Counter1 contents are transferred to the Input Cap-

ture Register (ICR1) on the rising edge of the Input Capture Pin (ICP).

• Bits 5, 4 – Res: Reserved Bits

These bits are reserved bits in the AT90S4433 and always read as zero.

• Bit 3 – CTC1: Clear Timer/Counter1 on Compare Match

When the CTC1 control bit is set (one), the Timer/Counter1 is reset to $0000 in the clock

cycle after a Compare Match. If the CTC1 control bit is cleared, Timer/Counter1 contin-

ues counting and is unaffected by a Compare Match. Since the compare match is

detected in the CPU clock cycle following the match, this function will behave differently

when a prescaling higher than 1 is used for the Timer. When a prescaling of 1 is used

and the Compare Register is set to C, the timer will count as follows if CTC1 is set:

... | C-2 | C-1 | C | 0 | 1 | ...

When the prescaler is set to divide by 8, the timer will count like this:

... | C-2, C-2, C-2, C-2, C-2, C-2, C-2, C-2 | C-1, C-1, C-1, C-1, C-1, C-1, C-1, C-1 | C, 0,

0, 0, 0, 0, 0, 0 | 1, 1, 1, 1, 1, 1, 1, 1| ...

In PWM mode, this bit has no effect.

Bit

$2E ($4E)

ICNC1

ICES1

–

CTC1

CS12

CS11

CS10

TCCR1B

Read/Write

R/W

Initial Value

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