ST10R272L - SYSTEM RESET
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worst-case discharge time needed for the internal or external oscillator to stabilize. See
“Selecting R and C values” on page 300 for the formula to calculate an appropriate value for
C. The value for R resistor must not interfere with the discharge current of the internal
pulldown device on RPD/Vpp pin. An R value between 200 kohms and 1Mohms should be
suitable
.
The minimum reset circuit of
Figure 111 is not adequate when the RSTIN pin is driven from
an external device, because of the capacitor C1 that will keep the voltage above V
IL
for short
low pulses applied on RSTIN pin.
Figure 10-5 shows an example of a system-reset circuit. In this example, R1C1 external
circuit is only used to generate power-up or manual reset, and RC circuit on RPD/Vpp is
used for power-up reset and to exit from powerdown mode. Diode D creates a wired-OR
gate connection to the reset pin and may be replaced by open-collector schmitt trigger
buffer. Diode D’ provides a faster cycle time for repetitive power-on resets.
R’ is an optional pull-up for faster recovery and correct biasing of TTL Open Collector
drivers.
Figure 112 System reset circuitry (example)
ST10R272L
External
Hardware
RSTOUT
+
RSTIN
RPD/Vpp
V
CC
C1
D
R1
D’
V
CC
R’
Open Drain Inverter
External
Reset Source
o.d.
+
VCC
C
R
