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ST72321 Datasheet(PDF) 26 Page - STMicroelectronics |
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ST72321 Datasheet(HTML) 26 Page - STMicroelectronics |
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26 / 189 page  ST72321 26/189 RESET SEQUENCE MANAGER (Cont’d) 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 characteris- tics section. If the external RESET pulse is shorter than tw(RSTL)out (see short ext. Reset in Figure 14), the signal on the RESET pin may be stretched. Other- wise the delay will not be applied (see long ext. Reset in Figure 14). Starting from the external RE- SET pulse recognition, the device RESET pin acts as an output that is pulled low during at least tw(RSTL)out. 6.3.3 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 VDD is over the minimum level specified for the selected fOSC frequency. (see “OPERATING CONDITIONS” on page 140) A proper reset signal for a slow rising VDD supply can generally be provided by an external RC net- work connected to the RESET pin. 6.3.4 Internal Low Voltage Detector (LVD) RESET Two different RESET sequences caused by the in- ternal LVD circuitry can be distinguished: ■ Power-On RESET ■ Voltage Drop RESET The device RESET pin acts as an output that is pulled low when VDD<VIT+ (rising edge) or VDD<VIT- (falling edge) as shown in Figure 14. The LVD filters spikes on VDD larger than tg(VDD) to avoid parasitic resets. 6.3.5 Internal Watchdog RESET The RESET sequence generated by a internal Watchdog counter overflow is shown in Figure 14. Starting from the Watchdog counter underflow, the device RESET pin acts as an output that is pulled low during at least tw(RSTL)out. Figure 14. RESET Sequences VDD RUN RESET PIN EXTERNAL WATCHDOG ACTIVE PHASE VIT+(LVD) VIT-(LVD) th(RSTL)in tw(RSTL)out RUN th(RSTL)in ACTIVE WATCHDOG UNDERFLOW tw(RSTL)out RUN RUN RUN RESET RESET SOURCE SHORT EXT. RESET LVD RESET LONG EXT. RESET WATCHDOG RESET INTERNAL RESET (256 or 4096 TCPU) VECTOR FETCH tw(RSTL)out PHASE ACTIVE PHASE ACTIVE PHASE DELAY |
Similar Part No. - ST72321_04 |
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Similar Description - ST72321_04 |
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