NOTE
PORST pin does not require active control. It is possible to
implement an external pull-up to ensure correct reset exit
sequence. Recommended value is 4.7 kohm.
PORST can optionally be connected to an external power-on
supply circuitry.
No restrictions exist on reset signal slew rate apart from
absolute maximum rating compliance.
V
IL
V
DD
V
DDMIN
PORST
V
IH
device start-up phase
V
DDPOR
PORST driven low
device reset
forced by external circuitry
PORST undriven
device reset by
by internal power-on reset
internal power-on reset
Figure 6. Start-up reset requirements
The following figure describes device behavior depending on supply signal on PORST:
1. PORST low pulse amplitude is too low—it is filtered by input buffer hysteresis.
Device remains in current state.
2. PORST low pulse duration is too short—it is filtered by a low pass filter. Device
remains in current state.
3. PORST low pulse is generating a reset:
• a) PORST low but initially filtered during at least W
FRST
. Device remains
initially in current state.
• b) PORST potentially filtered until W
NFRST
. Device state is unknown. It may
either be reset or remains in current state depending on extra condition
(temperature, voltage, device).
• c) PORST asserted for longer than W
NFRST
. Device is under reset.
Reset pad (PORST, RESET) electrical characteristics
SPC5746R Microcontroller Data Sheet, Rev. 6, 06/2017
NXP Semiconductors 19
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