st10f272z2 STMicroelectronics, st10f272z2 Datasheet - Page 96

• Manufacturer Part Number: st10f272z2
• Description: 16-bit Mcu With 256 Kbyte Flash Memory And 20 Kbyte Ram
• Manufacturer: STMicroelectronics

System reset
Note:
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The Bidirectional reset is not effective in case RPD is held low, when a Software or
Watchdog reset event occurs. On the contrary, if a Software or Watchdog Bidirectional reset
event is active and RPD becomes low, the RSTIN pin is immediately released, while the
internal reset sequence is completed regardless of RPD status change (1024 TCL).
The bidirectional reset function is disabled by any reset sequence (bit BDRSTEN of
SYSCON is cleared). To be activated again it must be enabled during the initialization
routine.
WDTCON flags
Similarly to what already highlighted in the previous section when discussing about Short
reset and the degeneration into Long reset, similar situations may occur when Bidirectional
reset is enabled. The presence of the internal filter on RSTIN pin introduces a delay: when
RSTIN is released, the internal signal after the filter (see RSTF in the drawings) is delayed,
so it remains still active (low) for a while. It means that depending on the internal clock
speed, a short reset may be recognized as a long reset: the WDTCON flags are set
accordingly.
Besides, when either Software or Watchdog bidirectional reset events occur, again when the
RSTIN pin is released (at the end of the internal reset sequence), the RSTF internal signal
(after the filter) remains low for a while, and depending on the clock frequency it is
recognized high or low: 8TCL after the completion of the internal sequence, the level of
RSTF signal is sampled, and if recognized still low a Hardware reset sequence starts, and
WDTCON will flag this last event, masking the previous one (Software or Watchdog reset).
Typically, a Short Hardware reset is recognized, unless the RSTIN pin (and consequently
internal signal RSTF) is sufficiently held low by the external hardware to inject a Long
Hardware reset. After this occurrence, the initialization routine is not able to recognize a
Software or Watchdog bidirectional reset event, since a different source is flagged inside
WDTCON register. This phenomenon does not occur when internal FLASH is selected
during reset (EA = 1), since the initialization of the FLASH itself extend the internal reset
duration well beyond the filter delay.
Next Figures 27,
Bidirectional reset events: In particular
reset.
28
and
29
summarize the timing for Software and Watchdog Timer
Figure 29
shows the degeneration into Hardware
ST10F272Z2