AT43USB325 datasheet(43/109 Pages) ATMEL

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3355C–USB–4/05

AT43USB325

6.2

8-bit Timer/Counter0

The 8-bit Timer/Counter0 can select clock source from CK, prescaled CK or an external pin. In

addition it can be stopped as described in the specification for the Timer/Counter0 Control Reg-

ister (TCCR0). The overflow status flag is found in the Timer/Counter Interrupt Flag Register

(TIFR). Control signals are found in the Timer/Counter0 Control Register (TCCR0). The interrupt

enable/disable settings for Timer/Counter0 are found in the Timer/Counter Interrupt Mask Regis-

ter - TIMSK.

When Timer/Counter0 is externally clocked, the external signal is synchronized with the oscilla-

tor 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 8-bit Timer/Counter0 features both a high resolution and a high accuracy usage with the

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

Timer/Counter0 useful for lower speed functions or exact timing functions with infrequent

actions.

Figure 6-2.

Timer/Counter0 Block Diagram

Control

Logic

Timer/Counter0

(TCNT0)

Timer Int. Mask Register

(TIMSK)

Timer Int. Flag Register

(TIFR)

T/C0 Control Register

(TCCR0)

T/C Clock Source

T/C0

Overflow IRQ

AT43USB325 Datasheet(PDF) 43 Page - ATMEL Corporation