AT43USB353M datasheet(43/95 Pages) ATMEL

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AT43USB353M

3307B–USB–4/04

Timer/Counter1 Input Capture Register – ICR1H and ICR1L

The input capture register is a 16-bit read-only register.

When the rising or falling edge (according to the input capture edge setting - ICES1) of the sig-

nal at the input capture pin (ICP) is detected, the current value of the Timer/Counter1 is

transferred to the Input Capture Register (ICR1). At the same time, the Input Capture Flag

(ICF1) is set (one).

Since the ICR1 is a 16-bit register, a temporary register TEMP is used when ICR1 is read to

ensure that both bytes are read simultaneously. When the CPU reads the low byte ICR1L, the

data is sent to the CPU and the data of the high byte ICR1H is placed in the TEMP register.

When the CPU reads the data in the high byte ICR1H, the CPU receives the data in the TEMP

operation.

The TEMP register is also used when accessing TCNT1, OCR1A and OCR1B. If the main pro-

gram and also interrupt routines perform access to registers using TEMP, interrupts must be

disabled during access from the main program and from interrupt routines, if interrupts are

allowed from within interrupt routines.

Timer/Counter1 In

PWM Mode

When the PWM mode is selected, Timer/Counter1, the Output Compare Register1A (OCR1A)

and the Output Compare Register1B (OCR1B) form a dual 8-, 9- or 10-bit, free-running, glitch-

fr ee and phas e c o rr ec t P W M wi th outputs on the P D 5 (OC1A) and OC1B pi ns.

Timer/Counter1 acts as an up/down counter, counting up from $0000 to TOP (see Table 17),

where it turns and counts down again to zero before the cycle is repeated. When the counter

value matches the contents of the 10 least significant bits of OCR1A or OCR1B, the

PD5(OC1A)/OC1B pins are set or cleared according to the settings of the COM1A1/COM1A0

or COM1B1/COM1B0 bits in the Timer/Counter1 Control Register TCCR1A. Refer to Table 18

for details.

Bit

$25 ($45)

MSB

–

–––

–

ICR1H

$24 ($44)

–

–––

–

LSB

ICR1L

543

Read/Write

Initial Value

000

Table 17. Timer TOP Values and PWM Frequency

PWM Resolution

Timer TOP value

Frequency

8-bit

$00FF (255)

fTCK1/510

9-bit

$01FF (511)

fTCK1/1022

10-bit

$03FF(1023)

fTCK1/2046

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