AT91SAM9R64_1 Datasheet, PDF (89/903 Pages) ATMEL Corporation – AT91 ARM Thumb Microcontrollers

AT91SAM9R64/RL64 Preliminary
15.3.4.2
Wake-up Reset
The Wake-up Reset occurs when the Main Supply is down. When the Main Supply POR output
is active, all the reset signals are asserted except backup_nreset. When the Main Supply pow-
ers up, the POR output is resynchronized on Slow Clock. The processor clock is then re-enabled
during 3 Slow Clock cycles, depending on the requirements of the ARM processor.
At the end of this delay, the processor and other reset signals rise. The field RSTTYP in
RSTC_SR is updated to report a Wake-up Reset.
The “nrst_out” remains asserted for EXTERNAL_RESET_LENGTH cycles. As RSTC_MR is
backed-up, the programmed number of cycles is applicable.
When the Main Supply is detected falling, the reset signals are immediately asserted. This tran-
sition is synchronous with the output of the Main Supply POR.
Figure 15-5. Wake-up State
SLCK
MCK
Any
Freq.
Main Supply
POR output
backup_nreset
proc_nreset
RSTTYP
periph_nreset
NRST
(nrst_out)
Resynch.
2 cycles
Processor Startup
= 3 cycles
XXX
0x1 = WakeUp Reset
EXTERNAL RESET LENGTH
= 4 cycles (ERSTL = 1)
XXX
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6289C–ATARM–28-May-09