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Supply, reset and clock management
ST7LITEUS2, ST7LITEUS5
Figure 12.
Reset block diagram
1.
Section 11.2.1: Illegal opcode reset
for more details on illegal opcode reset conditions
6.4.2
Asynchronous external RESET pin
The RESET pin is both an input and an open-drain output with integrated R
ON
weak pull-up
resistor. This pull-up has no fixed value but varies in accordance with the input voltage. It
can be pulled low by external circuitry to reset the device. See Electrical Characteristic
section for more details.
A RESET signal originating from an external source must have a duration of at least
t
h(RSTL)in
in order to be recognized (see
). This detection is asynchronous and
therefore the MCU can enter reset state even in Halt mode.
The RESET pin is an asynchronous signal which plays a major role in EMS performance. In
a noisy environment, it is recommended to follow the guidelines mentioned in the electrical
characteristics section.
6.4.3
External Power-on reset
If the LVD is disabled by option byte, to start up the microcontroller correctly, the user must
ensure by means of an external reset circuit that the reset signal is held low until V
DD
is over
the minimum level specified for the selected f
CLKIN
frequency.
A proper reset signal for a slow rising V
DD
supply can generally be provided by an external
RC network connected to the RESET pin.
6.4.4
Internal low voltage detector (LVD) reset
Two different reset sequences caused by the internal LVD circuitry can be distinguished:
●
Power-on reset
●
Voltage Drop reset
The device RESET pin acts as an output that is pulled low when V
DD
<V
IT+
(rising edge) or
V
DD
<V
IT-
(falling edge) as shown in
.
The LVD filters spikes on V
DD
larger than t
g(VDD)
to avoid parasitic resets.
RESET
R
ON
V
DD
INTERNAL
RESET
PULSE
GENERATOR
FILTER
LVD RESET
WATCHDOG RESET
ILLEGAL OPCODE RESET
1)
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