HT46RU22 Holtek Semiconductor Inc., HT46RU22 Datasheet - Page 11

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HT46RU22

Manufacturer Part Number
HT46RU22
Description
Ht46ru22 -- A/d Type 8-bit Mcu
Manufacturer
Holtek Semiconductor Inc.
Datasheet

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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.
Once the interrupt request flags, composed of TF, EIF,
ADF and HIF, are set, they will remain in the INTC0 and
INTC1 register until the interrupts are serviced or
cleared by a software instruction.
It is recommended that a program does not use the
rupts 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 con-
trolled, the original control sequence will be damaged
once the CALL operates in the interrupt subroutine.
Oscillator Configuration
There are two oscillator circuits in the microcontroller.
Both are designed for system clocks, namely the RC os-
cillator and the Crystal oscillator, which are determined
by the options. No matter what oscillator type is se-
lected, the signal provides the system clock. The HALT
Rev. 1.20
CALL subroutine within the interrupt subroutine. Inter-
External Interrupt
Timer/Event Counter Overflow
A/D Converter Interrupt
I
UART Interrupt
2
C Bus Interrupt
Interrupt Source
System Oscillator
Priority
1
2
3
4
5
Vector
0CH
04H
08H
10H
14H
Watchdog Timer
11
mode stops the system oscillator and ignores an exter-
nal signal to conserve power.
If an RC oscillator is used, an external resistor between
OSC1 and VSS is required and the resistance must
range from 24k to 1M . The system clock, divided by
4, is available on OSC2 with pull-high resistor, which
can be used to synchronize external logic. The RC os-
cillator provides the most cost effective solution. How-
ever, the frequency of oscillation may vary with VDD,
temperatures and the chip itself due to process varia-
tions. It is, therefore, not suitable for timing sensitive
operations where an 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 required for the oscillator, and no other external
components are required. Instead of a crystal, a resona-
tor 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 oscillating fre-
quency is less than 1MHz).
The WDT oscillator is a free running on-chip RC oscillator,
and no external components are required. Even if the sys-
tem enters the power down mode, the system clock is
stopped, but the WDT oscillator still works with a period of
approximately 65 s at 5V. The WDT oscillator can be dis-
abled by options to conserve power.
Watchdog Timer - WDT
The clock source of the WDT is implemented by an dedi-
cated RC oscillator (WDT oscillator) or instruction clock
(system clock divided by 4) decided by options. This
timer is designed to prevent a software malfunction or
sequence jumping to an unknown location with unpre-
dictable results. The watchdog Timer can be disabled by
an option. If the watchdog Timer is disabled, all the exe-
cutions related to the WDT result in no operation.
Once an internal WDT oscillator (RC oscillator with pe-
riod 65 s at 5V normally) is selected, it is divided by
2
minimum period of WDT time-out period is about
300ms~600ms. This time-out period may vary with tem-
12
~2
15
(by option to get the WDT time-out period). The
HT46RU22
March 23, 2007

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