HT46R62 Holtek Semiconductor Inc., HT46R62 Datasheet - Page 12

• Manufacturer Part Number: HT46R62
• Description: Ht46r62/ht46c62 -- A/d With Lcd Type 8-bit Mcu
• Manufacturer: Holtek Semiconductor Inc.

terrupt control bit are set both to 1 (if the stack is not full).
To return from the interrupt subroutine, RET or RETI
may be invoked. RETI sets the EMI bit and enables an
interrupt service, but RET does not.
Interrupts occurring in the interval between the rising
edges of two consecutive T2 pulses are serviced on the
latter of the two T2 pulses if the corresponding interrupts
are enabled. In the case of simultaneous requests, the
priorities in the following table apply. These can be
masked by resetting the EMI bit.
The Timer/Event Counter interrupt request flag (TF), ex-
ternal interrupt 1 request flag (EIF1), external interrupt 0
request flag (EIF0), enable Timer/Event Counter inter-
rupt bit (ETI), enable external interrupt 1 bit (EEI1), en-
able external interrupt 0 bit (EEI0) and enable master
interrupt bit (EMI) make up of the Interrupt Control regis-
ter 0 (INTC0) which is located at 0BH in the RAM. The
real time clock interrupt request flag (RTF), time base in-
terrupt request flag (TBF), enable real time clock inter-
rupt bit (ERTI), and enable time base interrupt bit
(ETBI), on the other hand, constitute the Interrupt Con-
trol register 1 (INTC1) which is located at 1EH in the
RAM. EMI, EEI0, EEI1, ETI, ET1I, ETBI and ERTI are all
used to control the enable/disable status of interrupts.
These bits prevent the requested interrupt from being
serviced. Once the interrupt request flags (RTF, TBF,
TF, EIF1, EIF0) are all set, they remain in the INTC1 or
INTC0 respectively until the interrupts are serviced or
cleared by a software instruction.
It is recommended that a program should not use the
cause interrupts often occur in an unpredictable manner
or require to be serviced immediately in some applica-
tions. During that period, if only one stack is left, and en-
abling the interrupt is not well controlled, operation of
the call in the interrupt subroutine may damage the
original control sequence.
Oscillator Configuration
The device provides three oscillator circuits for system
clocks, i.e., RC oscillator, crystal oscillator and 32768Hz
crystal oscillator, determined by options. No matter what
type of oscillator is selected, the signal is used for the
system clock. The HALT mode stops the system oscilla-
tor (RC and crystal oscillator only) and ignores external
signal in order to conserve power. The 32768Hz crystal
oscillator still runs at HALT mode. If the 32768Hz crystal
Rev. 1.70
CALL subroutine within the interrupt subroutine. It s be-
External interrupt 0
External interrupt 1
Timer/Event Counter overflow
Time base interrupt
Real time clock interrupt
Interrupt Source
Priority
1
2
3
4
5
Vector
0CH
04H
08H
14H
18H
12
Note:
oscillator is selected as the system oscillator, the system
oscillator is not stopped; but the instruction execution is
stopped. Since the 32768Hz oscillator is also designed
for timing purposes, the internal timing (RTC, time base,
WDT) operation still runs even if the system enters the
HALT mode.
Of the three oscillators, if the RC oscillator is used, an
external resistor between OSC1 and VSS is required,
and the range of the resistance should be from 30k to
750k . The system clock, divided by 4, is available on
OSC2 with pull-high resistor, 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.
On the other hand, if the crystal oscillator is selected, 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. A resonator
may be connected between OSC1 and OSC2 to replace
the crystal and to get a frequency reference, but two ex-
ternal capacitors in OSC1 and OSC2 are required.
There is another oscillator circuit designed for the real
time clock. In this case, only the 32.768kHz crystal oscil-
lator can be applied. The crystal should be connected
between OSC3 and OSC4.
32768Hz crystal enable condition: For WDT
clock source or for system clock source.
The external resistor and capacitor components
connected to the 32768Hz crystal are not neces-
sary to provide oscillation. For applications
where precise RTC frequencies are essential,
these components may be required to provide
frequency compensation due to different crystal
manufacturing tolerances.
System Oscillator
HT46R62/HT46C62
February 14, 2006