H49R50A-1 Datasheet, PDF (13/45 Pages) Holtek Semiconductor Inc – LCD Type 8-Bit MCU

HT49R50A-1/HT49C50-1/HT49C50L
The Timer/Event Counter 0 interrupt request flag (T0F),
external interrupt 1 request flag (EIF1), external inter-
rupt 0 request flag (EIF0), enable Timer/Event Counter
0 interrupt bit (ET0I), enable external interrupt 1 bit
(EEI1), enable external interrupt 0 bit (EEI0), and en-
able master interrupt bit (EMI) make up of the Interrupt
Control register 0 (INTC0) which is located at 0BH in the
RAM. The real time clock interrupt request flag (RTF),
time base interrupt request flag (TBF), Timer/Event
Counter 1 interrupt request flag (T1F), enable real time
clock interrupt bit (ERTI), and enable time base interrupt
bit (ETBI), enable Timer/Event Counter 1 interrupt bit
(ET1I) on the other hand, constitute the Interrupt Control
register 1 (INTC1) which is located at 1EH in the RAM.
EMI, EEI0, EEI1, ET0I, 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, T0F,
T1F, 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 not use the ²CALL
subroutine² within the interrupt subroutine. It¢s because
interrupts often occur in an unpredictable manner or re-
quire to be serviced immediately in some applications.
At this time, if only one stack is left, and enabling the in-
terrupt is not well controlled, operation of the ²call² in the
interrupt subroutine may damage the original control se-
quence.
Oscillator Configuration
These devices provide three oscillator circuits for sys-
tem clocks, i.e., RC oscillator and crystal oscillator, de-
termined by option. No matter what type of oscillator is
selected, the signal is used for the system clock. The
HALT mode stops the system oscillator and ignores ex-
ternal signal to conserve power.
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 30kW to
750kW for HT49R50A-1/HT49C50-1 and from 560kW to
1MW for HT49C50L. The system clock, divided by 4, is
available on OSC2 with pull-high resistor, which can be
used to synchronize external logic. The RC oscillator
provides the most cost effective solution. However, the
frequency of the oscillation may vary with VDD, temper-
ature, 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.
O SC1
V DD
O SC1
V DD
O SC2
C r y s ta l O s c illa to r
fS Y S /4
System Oscillator
O SC2
R C O s c illa to r
O SC3
O SC4
32768Hz Crystal/RTC Oscillator
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, and two external capacitors
along with one external resistor are required for the os-
cillator circuit in order to get a stable frequency.
The RTC oscillator circuit can be controlled to oscillate
quickly by setting the ²QOSC² bit (bit 4 of RTCC). It is
recommended to turn on the quick oscillating function
upon power on, and turn it off after 2 seconds.
The WDT oscillator is a free running on-chip RC oscilla-
tor, and no external components are required. Although
the system enters the power down mode, the system
clock stops, and the WDT oscillator still works with a pe-
riod of approximately 65ms@5V. The WDT oscillator can
be disabled by option to conserve power.
Watchdog Timer - WDT
The WDT clock source is implemented by a dedicated
RC oscillator (WDT oscillator) or an instruction clock
(system clock/4) or a real time clock oscillator (RTC os-
cillator). The timer is designed to prevent a software
malfunction or sequence from jumping to an unknown
location with unpredictable results. The WDT can be
disabled by option. But if the WDT is disabled, all execu-
tions related to the WDT lead to no operation.
The WDT time-out period is as f_S/2¹⁶~f_S/2¹⁵.
If the WDT clock source chooses the internal WDT oscilla-
tor, the time-out period may vary with temperature, VDD,
and process variations. On the other hand, if the clock
source selects the instruction clock and the ²HALT² in-
struction is executed, WDT may stop counting and lose its
protecting purpose, and the logic can only be restarted by
an external logic.
Rev. 2.00
13
November 29, 2005