Datasheet

179
32133D–11/2011
UC3D
14. Asynchronous Timer (AST)
Rev: 3.1.0.1
14.1 Features
• 32-bit counter with 32-bit prescaler
• Clocked Source
– System RC oscillator (RCSYS)
– 32KHz crystal oscillator (OSC32K)
–PB clock
– Generic clock (GCLK)
• Optional calendar mode supported
• Periodic interrupt(s) supported
• Alarm interrupt(s) supported
– Optional clear on alarm
14.2 Overview
The Asynchronous Timer (AST) enables periodic interrupts, as well as interrupts 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 five different clock sources, including the low-power 32KHz oscil-
lator, 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 from output from the prescaler, as well as alarm inter-
rupts, which can trigger at any counter value. Additionally, the timer can trigger an overflow
interrupt, and be reset on the occurrence of any alarm. This allows periodic interrupts 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.