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HT48C30-1 Datasheet(PDF) 10 Page - Holtek Semiconductor Inc |
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HT48C30-1 Datasheet(HTML) 10 Page - Holtek Semiconductor Inc |
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10 / 40 page  HT48R30A-1/HT48C30-1 Rev. 1.90 10 November 4, 2005 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 inter- rupts are enabled. In the case of simultaneous requests the following table shows the priority that is applied. These can be masked by resetting the EMI bit. No. Interrupt Source Priority Vector a External Interrupt 1 04H b Timer/Event Counter Overflow 2 08H The timer/event counter interrupt request flag (TF), ex- ternal interrupt request flag (EIF), enable timer/event counter interrupt bit (ETI), enable external interrupt bit (EEI) and enable master interrupt bit (EMI) constitute an interrupt control register (INTC) which is located at 0BH in the data memory. EMI, EEI, ETI are used to control the enabling/disabling of interrupts. These bits prevent the requested interrupt from being serviced. Once the interrupt request flags (TF, EIF) are set, they will remain in the INTC register until the interrupts are serviced or cleared by a software instruction. It is recommended that a program does not use the ²CALL subroutine² within the interrupt subroutine. In- terrupts 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, the original control sequence will be dam- aged once the ²CALL² operates in the interrupt subrou- tine. Oscillator Configuration There are 3 oscillator circuits in the microcontroller. All of them are designed for system clocks, namely the external RC oscillator, the external Crystal oscillator and the internal RC oscillator, which are determined by op- tions. No matter what oscillator type is selected, the sig- nal provides the system clock. The HALT mode stops the system oscillator and ignores an external signal to conserve power. If an RC oscillator is used, an external resistor between OSC1 and VDD is required and the resistance must range from 24k W to 1MW. The system clock, divided by 4, is available on OSC2, which can be used to synchro- nize external logic. The RC oscillator provides the most cost effective solution. However, the frequency of oscil- lation may vary with VDD, temperatures and the chip it- self due to process variations. It is, therefore, not suitable for timing sensitive operations where an accu- rate 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 required for the oscillator. No other external compo- nents are required. In stead of a crystal, a resonator can also be connected between OSC1 and OSC2 to get a frequency reference, but two external capacitors in OSC1 and OSC2 are required. If the internal RC oscilla- tor is used, the OSC1 and OSC2 can be selected as general I/O lines or an 32768Hz crystal oscillator (RTC OSC). Also, the frequencies of the internal RC oscillator can be 3.2MHz, 1.6MHz, 800kHz and 400kHz (depends on the options). 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 oscillator still works within a pe- riod of 65 ms at 5V. The WDT oscillator can be disabled by options to conserve power. Bit No. Label Function 0 EMI Controls the master (global) interrupt (1= enabled; 0= disabled) 1 EEI Controls the external interrupt (1= enabled; 0= disabled) 2 ETI Controls the Timer/Event Counter 0 interrupt (1= enabled; 0= disabled) 3 ¾ Unused bit, read as ²0² 4 EIF External interrupt request flag (1= active; 0= inactive) 5 TF Internal Timer/Event Counter 0 request flag (1= active; 0= inactive) 6 ¾ Unused bit, read as ²0² 7 ¾ Unused bit, read as ²0² INTC (0BH) Register C r y s t a l O s c i l l a t o r ( I n c l u d e 3 2 7 6 8 H z ) R C O s c i l l a t o r O S C 1 O S C 2 N M O S O p e n D r a i n O S C 2 f S Y S / 4 4 7 0 p F V D D O S C 1 System Oscillator |
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