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What isPOR, LVD and WDT                   1
Power-On Reset   Definition: Restoring a device, register, or memory to a predetermined state when power is       applied....
Power-On Reset (cont)  VCC [V]     Vdet                                              time Internal state in    CPU Reset  ...
Low-voltage Detection•   Definition: Detection of supply voltage cut-off and brownouts.•   It monitors the supply voltage ...
Low-voltage Detection (cont)  VCC [V]                                                              Brownout           5.0 ...
Watchdog Timer•   Used mainly to reset MCU during program runaway or other incorrect program    execution.•   When the WDT...
Watchdog Timer (cont)Count = H’FF (maximum) Count = 0                                                                    W...
For more Tutorials   •    www.pantechsolutions.net   •    http://www.slideshare.net/pantechsolutions   •    http://www.scr...
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What is POR,LVD,WDT ?

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Definition of power on reset,low voltage detection,watch dog timer.

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What is POR,LVD,WDT ?

  1. 1. What isPOR, LVD and WDT 1
  2. 2. Power-On Reset Definition: Restoring a device, register, or memory to a predetermined state when power is applied. • Ensuring that the MCU starts at a known address with registers in defined state when power is first applied. • POR circuit is required to assert the RESET signal only when supply voltage has stabilised reach a minimum required voltage. • Clock oscillations should also be stabilised before asserting RESET signal. • Failure to carry out a proper POR may result in registers and memory contents of MCUs in undetermined/incorrect states. It can cause MCUs to fail or be in an unrecoverable state. • External POR circuits (e.g. RC circuit) or internal POR circuit with voltage comparator and timer to delay the RESET signal when voltage level is reached5/24/2011 9:01:20 © Pantech Solutions Pvt Ltd. | All rights reserved www.pantechsolutions.netPM
  3. 3. Power-On Reset (cont) VCC [V] Vdet time Internal state in CPU Reset Reset Released Reset delay VCC [V] time 3
  4. 4. Low-voltage Detection• Definition: Detection of supply voltage cut-off and brownouts.• It monitors the supply voltage and generates an internal Reset or Interrupt when that voltage drops too low.• In some cases, after voltage drops below a predefined value, the voltage is monitored for a few clock cycles to ensure voltage drop is not due to noise/glitches.• The Reset or Interrupt can be used to safely power the system down or back up memory before shutdown etc. 4
  5. 5. Low-voltage Detection (cont) VCC [V] Brownout 5.0 Vdet Vdet = 3.8V ± 0.5V 2.7 Power supply cut-off timeInternalstate in Reset Released CPU Reset Reset Released Reset Interrupt 5
  6. 6. Watchdog Timer• Used mainly to reset MCU during program runaway or other incorrect program execution.• When the WDT underflows, either a Watchdog Timer Interrupt or a Reset can be generated.• The application program could periodically reload the WDT timer before it underflows to ensure that an interrupt or reset isn’t generated. If the program goes out of control, this periodic reload would not happen. Therefore, the WDT would generate either an interrupt or a Reset that would cause the application program to revert to a known (safe or preferred) state. 6
  7. 7. Watchdog Timer (cont)Count = H’FF (maximum) Count = 0 Watchdog Overflows Watchdog Timer starts User program resets WDT counter or set to other values so that it does not overflow Internal Reset Signal Reset Generated 7
  8. 8. For more Tutorials • www.pantechsolutions.net • http://www.slideshare.net/pantechsolutions • http://www.scribd.com/pantechsolutions • http://www.youtube.com/pantechsolutions5/24/2011 9:00:19 © Pantech Solutions Pvt Ltd. | All rights reserved www.pantechsolutions.netPM

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