Datasheet

134
32117D–AVR-01/12
AT32UC3C
9. Asynchronous Timer (AST)
Rev: 2.0.0.1
9.1 Features
• 32-bit counter with 32-bit prescaler
• Clocked Source
– System RC oscillator (RCSYS)
– 32KHz crystal oscillator (OSC32K)
–PB clock
– Generic clock (GCLK)
– 1KHz clock from 32KHz oscillator
• Optional calendar mode supported
• Digital prescaler tuning for increased accuracy
• Periodic interrupt(s) and peripheral event(s) supported
• Alarm interrupt(s) and peripheral event(s) supported
– Optional clear on alarm
9.2 Overview
The Asynchronous Timer (AST) enables periodic interrupts and periodic peripheral events, as
well as interrupts and peripheral events at a specified time in the future. The AST consists of a
32-bit prescaler which feeds a 32-bit up-counter. The prescaler can be clocked from four differ-
ent clock sources, including the low-power 32KHz clock, which allows the AST to be used as a
real-time timer with a maximum timeout of more than 100 years. Also, the PB clock or a generic
clock can be used for high-speed operation, allowing the AST to be used as a general timer.
The AST can generate periodic interrupts and peripheral events from output from the prescaler,
as well as alarm interrupts and peripheral events, which can trigger at any counter value. Addi-
tionally, the timer can trigger an overflow interrupt and peripheral event, and be reset on the
occurrence of any alarm. This allows periodic interrupts and peripheral events at very long and
accurate intervals.
The AST has been designed to meet the system tick and Real Time Clock requirements of most
embedded operating systems.