at91cap7e ATMEL Corporation, at91cap7e Datasheet - Page 68

• Manufacturer Part Number: at91cap7e
• Description: Customizable Microcontroller
• Manufacturer: ATMEL Corporation

14.3.2
Figure 14-2. NRST Manager
14.3.2.1
14.3.2.2
68
AT91CAP7E
NRST Manager
NRST Signal or Interrupt
NRST External Reset Control
NRST
The startup counter waits for the complete crystal oscillator startup. The wait delay is given by
the crystal oscillator startup time maximum value that can be found in the section Crystal Oscil-
lator Characteristics in the Electrical Characteristics section of the product documentation.
The Reset Controller Mode Register (RSTC_MR), allowing the configuration of the Reset Con-
troller, is powered with VDDBU, so that its configuration is saved as long as VDDBU is on.
The NRST Manager samples the NRST input pin and drives this pin low when required by the
Reset State Manager.
The NRST Manager samples the NRST pin at Slow Clock speed. When the line is detected low,
a User Reset is reported to the Reset State Manager.
However, the NRST Manager can be programmed to not trigger a reset when an assertion of
NRST occurs. Writing the bit URSTEN at 0 in RSTC_MR disables the User Reset trigger.
The level of the pin NRST can be read at any time in the bit NRSTL (NRST level) in RSTC_SR.
As soon as the pin NRST is asserted, the bit URSTS in RSTC_SR is set. This bit clears only
when RSTC_SR is read.
The Reset Controller can also be programmed to generate an interrupt instead of generating a
reset. To do so, the bit URSTIEN in RSTC_MR must be written at 1.
The Reset State Manager asserts the signal ext_nreset to assert the NRST pin. When this
occurs, the “nrst_out” signal is driven low by the NRST Manager for a time programmed by the
field ERSTL in RSTC_MR. This assertion duration, named EXTERNAL_RESET_LENGTH, lasts
2
and 2 seconds. Note that ERSTL at 0 defines a two-cycle duration for the NRST pulse.
This feature allows the Reset Controller to shape the NRST pin level, and thus to guarantee that
the NRST line is driven low for a time compliant with potential external devices connected on the
system reset.
(ERSTL+1)
Slow Clock cycles. This gives the approximate duration of an assertion between 60 μs
RSTC_SR
nrst_out
URSTS
NRSTL
Figure 14-2
External Reset Timer
RSTC_MR
RSTC_MR
ERSTL
URSTEN
shows the block diagram of the NRST Manager.
RSTC_MR
URSTIEN
interrupt
sources
Other
user_reset
exter_nreset
rstc_irq
8549A–CAP–10/08