XC886/888CLM
Power Supply, Reset and Clock Management
User’s Manual
7-3
V1.3, 2010-02
Power, Reset and Clock, V 1.0
7.2
Reset Control
The XC886/888 has five types of resets: power-on reset, hardware reset, watchdog timer
reset, power-down wake-up reset, and brownout reset.
When the XC886/888 is first powered up, the status of certain pins (see
be defined to ensure proper start operation of the device. At the end of a reset sequence,
the sampled values are latched to select the desired boot option, which cannot be
modified until the next power-on reset or hardware reset. This guarantees stable
conditions during the normal operation of the device.
The hardware reset function can be used during normal operation or when the chip is in
power-down mode. A reset input pin RESET is provided for the hardware reset.
The Watchdog Timer (WDT) module is also capable of resetting the device if it detects
a malfunction in the system.
Another type of reset that needs to be detected is the reset while the device is in
power-down mode (i.e., wake-up reset). While the contents of the static RAM are
undefined after a power-on reset, they are well defined after a wake-up reset from
power-down mode.
A brownout reset is triggered if the
V
DDC
supply voltage dips below 2.1 V.
7.2.1
Types of Resets
7.2.1.1
Power-On Reset
The supply voltage
V
DDP
is used to power up the chip. The EVR is the first module in the
chip to be reset, which includes:
1. Startup of the main voltage regulator and the low power voltage regulator.
2. When
V
DDP
and
V
DDC
reach the threshold of the
V
DDP
and
V
DDC
detectors, the reset of
EVR becomes inactive.
In order to power up the system properly, the external reset pin RESET must be asserted
until
V
DDC
reaches 0.9*
V
DDC
. The delay of external reset can be realized by an external
capacitor at RESET pin. This capacitor value must be selected so that
V
RESET
reaches
0.4 V, but not before
V
DDC
reaches 0.9*
V
DDC.
A typical application example is shown in
V
DDP
capacitor value is 100 nF
while the
V
DDC
capacitor value is 220 nF. The capacitor connected to RESET pin is
100 nF.
Typically, the time taken for
V
DDC
to reach 0.9*
V
DDC
is less than 50
µ
s once
V
DDP
reaches
2.3V (based on the condition that 10% to 90%
V
DDP
(slew rate) is less than 500
µ
s). See
*
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