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HT82K68E-L Datasheet(PDF) 10 Page - Holtek Semiconductor Inc |
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HT82K68E-L Datasheet(HTML) 10 Page - Holtek Semiconductor Inc |
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10 / 38 page  HT82K68E-L/HT82K68A-L Rev. 1.30 10 August 5, 2009 During the execution of an interrupt subroutine, other in- terrupt acknowledgements are held until the RETI in- struction is executed or the EMI bit and the related interrupt control bit are set to 1 (if the stack is not full). To return from the interrupt subroutine, a RET or RETI in- struction may be invoked. RETI will set the EMI bit to en- able an interrupt service, but RET will not. Interrupts occurring in the interval between the rising edges of two consecutive T2 pulses, will be serviced on the latter of the two T2 pulses, if the corresponding interrupts are enabled. In the case of simultaneous re- quests, the following table shows the priority that is ap- plied. These can be masked by resetting the EMI bit. Interrupt Source Vector External interrupt 1 04H Timer counter overflow 08H Once the interrupt request flags (T0F) are set, they will remain in the INTC register until the interrupts are ser- viced or cleared by a software instruction. It is suggested that a program does not use the ²CALL subroutine ² within the interrupt subroutine. Because interrupts often occur in an unpredictable manner or need to be serviced immediately in some applications, if only one stack is left and enabling the interrupt is not well controlled, once the ²CALL subroutine² operates in the interrupt subroutine it will damage the original con- trol sequence. Oscillator Configuration There are two oscillator circuits in the microcontroller. Both are designed for system clocks; the RC oscillator and the Crystal oscillator, which are determined by mask options. No matter what oscillator type is selected, the signal provides the system clock. The HALT mode stops the system oscillator and resists the external signal to conserve power. If an RC oscillator is used, an external resistor between OSC1 and VDD is needed and the resistance must range from 20k W to 510kW. The system clock, divided by 4, is available on OSC2, which can be used to syn- chronize external logic. The RC oscillator provides the most cost effective solution. However, the frequency of the oscillation may vary with VDD, temperature and the chip itself due to process variations. It is, therefore, not suitable for timing sensitive operations where accurate oscillator frequency is desired. If the Crystal oscillator is used, a crystal across OSC1 and OSC2 is needed to provide the feedback and phase shift needed for oscillator, no other external components are needed. Instead of a crystal, the resonator can also be connected between OSC1 and OSC2 to get a fre- quency reference, but two external capacitors in OSC1 and OSC2 are required. The WDT oscillator is a free running on-chip RC oscilla- tor, and no external components are required. Even if the system enters the power down mode, the system clock is stopped, but the WDT oscillator still works for a period of approximately 78 ms. The WDT oscillator can be disabled by mask option to conserve power. Watchdog Timer - WDT The WDT clock source is implemented by a dedicated RC oscillator (WDT oscillator) or instruction clock (sys- tem clock divided by 4), decided by mask options. This timer is designed to prevent a software malfunction or se- quence jumping to an unknown location with unpredict- able results. The Watchdog Timer can be disabled by mask option. If the Watchdog Timer is disabled, all the ex- ecutions related to the WDT results in no operation. Once the internal WDT oscillator (RC oscillator normally with a period of 78 ms) is selected, it is first divided by 256 (8-stages) to get the nominal time-out period of approxi- mately 20ms. This time-out period may vary with temper- ature, VDD and process variations. By invoking the WDT prescaler, longer time-out periods can be realized. Writ- ing data to WS2, WS1, WS0 (bit 2,1,0 of the WDTS) can give different time-out periods. If WS2, WS1, WS0 are all equal to 1, the division ratio is up to 1:128, and the maxi- mum time-out period is 2.6 seconds. S y s t e m c l o c k / 4 8 - b i t C o u n t e r W D T P r e s c a l e r 7 - b i t C o u n t e r 8 - t o - 1 M U X W D T T i m e - o u t W S 0 ~ W S 2 M a s k O p t i o n S e l e c t W D T O S C Watchdog Timer C r y s t a l O s c i l l a t o r R C O s c i l l a t o r O S C 1 O S C 2 O S C 1 O S C 2 V D D f S Y S / 4 ( N M O S O p e n D r a i n O u t p u t ) System Oscillator |
Similar Part No. - HT82K68E-L_09 |
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Similar Description - HT82K68E-L_09 |
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