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HT56R22 Datasheet(PDF) 35 Page - Holtek Semiconductor Inc |
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HT56R22 Datasheet(HTML) 35 Page - Holtek Semiconductor Inc |
35 / 127 page HT56R22/HT56R23/HT56R24/HT56R25/HT56R26 Rev. 1.30 35 December 26, 2014 M I S C R e g i s t e r b 7 W D T E N 0 b 0 W D T E N 1 P A 0 ~ P A 3 O p e n D r a i n C o n t r o l - d e s c r i b e d e l s e w h e r e W a t c h d o g T i m e r E n a b l e C o n t r o l O D E 0 W D T E N 3 1 W D T E N 2 W D T E N 3 O D E 1 O D E 2 O D E 3 W D T E N 2 0 W D T E N 1 1 W D T E N 0 0 d i s a b l e e n a b l e a l l o t h e r v a l u e s Watchdog Timer Software Control - MISC If the fSYS/4 clock is used as the Watchdog Timer clock source, it should be noted that when the system enters the Power Down Mode, then the instruction clock is stopped and the Watchdog Timer will lose its protecting purposes. For systems that operate in noisy environ- ments, using the LIRC oscillator is strongly recom- mended. Under normal program operation, a Watchdog Timer time-out will initialise a device reset and set the status bit TO. However, if the system is in the Power Down Mode, when a Watchdog Timer time-out occurs, the TO bit in the status register will be set and only the Program Counter and Stack Pointer will be reset. Three methods can be adopted to clear the contents of the Watchdog Timer. The first is an external hardware reset, which means a low level on the RES pin, the second is using the watchdog software instructions and the third is via a ²HALT² instruction. Clearing the Watchdog Timer There are two methods of using software instructions to clear the Watchdog Timer, one of which must be chosen by configuration option. The first option is to use the sin- gle ²CLR WDT² instruction while the second is to use the two commands ²CLR WDT1² and ²CLR WDT2². For the first option, a simple execution of ²CLR WDT² will clear the WDT while for the second option, both ²CLR WDT1² and ²CLR WDT2² must both be executed to successfully clear the Watchdog Timer. Note that for this second op- tion, if ²CLR WDT1² is used to clear the Watchdog Timer, successive executions of this instruction will have no ef- fect, only the execution of a ²CLR WDT2² instruction will clear the Watchdog Timer. Similarly after the ²CLR WDT2 ² instruction has been executed, only a successive ²CLR WDT1² instruction can clear the Watchdog Timer. |
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