ST10R272L - SYSTEM RESET
264/320
The simplest way to reset the ST10R272L, is to insert a capacitor between RSTIN pin and
Vss (C1 in
Figure 107), plus a capacitor between RPD/Vpp pin and Vss (C2) and a pull-up
between RPD/Vpp pin and Vcc. The input RSTIN provides an internal pullup device
equalling a resistor of 50-250 kOhms (the minimum reset time must be determined by the
lowest value). Select C1 that produce a sufficient discharge time to permit the internal or
external oscillator and/or internal PLL to stabilize.
An asynchronous hardware reset is required during power-up, to guarantee correct
power-up reset with controlled supply current consumption (especially if the clock signal
requires a long stabilization time). It is recommended to connect the external RC circuit
shown in
Figure 111 to the RPD/Vpp pin. On power-up, the logical low level on RPD/Vpp pin
forces an asynchronous hardware reset when RSTIN is asserted. The external pull-up will
then charge the capacitor C. Note that an internal pull-down device on RPD/Vpp pin is
turned on when RSTIN pin is low, and causes the external capacitor (C) to begin discharging
at a typical rate of 100µA to 200 µA. With this mechanism, after power-up reset, short low
pulses applied on RSTIN produce synchronous hardware reset, but if RSTIN is asserted
longer than the time needed for C to be discharged by the internal pull-down device, then the
hardware reset starts in a synchronous manner if a clock is applied, but is then forced in an
asynchronous manner. This mechanism insures recovery from very catastrophic failure.
The external C capacitor on RPD/Vpp pin is also used to exit from Powerdown mode with
external interrupt. In this case, select components that produce a sufficient discharge time to
permit the internal or external oscillator circuitry to stabilize. If exiting powerdown mode is
only done by hardware reset, the capacitor C must be selected by determining the
Figure 111 Minimum external reset circuitry
ST10R272L
External
Hardware
RSTOUT
+
RSTIN
+
RPD/Vpp
VCC
a) Hardware Reset
C1
C
b) For Power-up Reset
(and Interruptible Power-
down mode)
R