157
32099I–01/2012
AT32UC3L016/32/64
Communication between the synchronous clock domains is disturbed when entering and exiting
sleep modes. Bus transactions over clock domains affected by the sleep mode are therefore not
recommended. The system may hang if the bus clocks are stopped during a bus transaction.
The CPU is automatically stopped in a safe state to ensure that all CPU bus operations are com-
plete when the sleep mode goes into effect. Thus, when entering Idle mode, no further action is
necessary.
When entering a sleep mode (except Idle mode), all HSB masters must be stopped before
entering the sleep mode. In order to let potential PBx write operations complete, the user should
let the CPU perform a PBx register read operation before issuing the sleep instruction. This will
stall the CPU until pending PBx operations have completed.
The Shutdown sleep mode requires extra care. Please refer to
Section 12.6.4.12.6.4
Shutdown Sleep Mode
12.6.4.1
Description
The Shutdown sleep mode is available only when the device is used in the “3.3V supply mode,
with 1.8V regulated I/O lines“ configuration (refer to the Power Considerations chapter). In this
configuration, the voltage regulator supplies both VDDCORE and VDDIO power supplies.
When the device enters Shutdown mode, the regulator is turned off and only the following logic
is kept powered by VDDIN:
– OSC32K using alternate pinout PA13/PA20
– AST core logic (internal counter and alarm detection logic)
– Backup Registers
– I/O lines PA11, PA13, PA20, PA21, PB04, PB05, and PB10
– RESET_N line
The table below lists I/O line functionality that remains operational during Shutdown sleep mode.
If no special function is used the I/O line will keep its setting when entering the sleep mode
12.6.4.2
Entering Shutdown sleep mode
Before entering the Shutdown sleep mode, a few actions are required:
– All modules should normally be disabled before entering Shutdown sleep mode (see
Table 12-4.
I/O Lines Usage During Shutdown Mode
Pin
Possible Usage During Shutdown Sleep Mode
PA11
WAKE_N signal (active low wake-up)
PA13
XIN32_2 (OSC32K using alternate pinout)
PA20
XOUT32_2 (OSC32K using alternate pinout)
PA21
PB04
PB05
PB10
RESET_N
Reset pin