Datasheet

135
32117D–AVR-01/12
AT32UC3C
9.3 Block Diagram
Figure 9-1. Asynchronous Timer block diagram
9.4 Product Dependencies
In order to use this module, other parts of the system must be configured correctly, as described
below.
9.4.1 Power Management
When the AST is enabled, it will remain clocked as long as its selected clock source is running. It
can also wake the CPU from the currently active sleep mode. Refer to the Power Manager chap-
ter for details on the different sleep modes.
9.4.2 Clocks
The clock for the AST bus interface (CLK_AST) is generated by the Power Manager. This clock
is turned on by default, and can be enabled and disabled in the Power Manager.
A number of clocks can be selected as source for the internal prescaler clock CLK_AST_PRSC.
The prescaler, counter, and interrupt will function as long as this selected clock source is active.
The selected clock must be enabled in the System Control Interface (SCIF).
The following clock sources are available:
• System RC oscillator (RCSYS). This oscillator is always enabled, except in some sleep
modes. Please refer to the Electrical Characteristics chapter for the characteristic frequency
of this oscillator.
• 32KHz crystal oscillator (OSC32K). This oscillator must be enabled before use.
32-bit
Prescaler
RC OSC
32-bit
counter
Alarm
Interrupts
COUNTER
VALUE
OVF
32 KHz
CONTROL REGISTER
EN
CSSEL
PSEL
CLK_AST_PRSC
PB clock
GCLK
Periodic
Interrupts
ALARM
REGISTER
Interrupt
Control
IRQs
PERIODIC
INTERVAL
REGISTER
Events
Wake
Control
Wake
WAKE ENABLE
REGISTER
DIGITAL
TUNER
REGISTER
CLK_AST
CLK_AST
CLK_AST
CLK_AST_CNT