參數(shù)資料
型號(hào)： HT46R64
廠商： Holtek Semiconductor Inc.
英文描述： A/D with LCD Type 8-Bit MCU
中文描述： 在A / D液晶型8位微控制器
文件頁(yè)數(shù)： 13/47頁(yè)
文件大?。?/td> 345K
代理商： HT46R64
HT46R64/HT46C64
Rev. 1.40
13
September 21, 2004
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
crystalacrossOSC1andOSC2isneededtoprovidethe
feedback and phase shift required for the oscillator, and
no other external components are required. Aresonator
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.
The RTC oscillator circuit can be controlled to oscillate
quickly by setting the QOSC bit (bit 4 of RTCC). It is
recommended to turn on the quick oscillating function
upon power on, and then 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 65 s at 5V. The WDT oscillator
can be disabled by options 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 options. But if the WDT is disabled, all exe-
cutions related to the WDT lead to no operation.
Once an internal WDT oscillator (RC oscillator with pe-
riod 65 s at 5V normally) is selected, it is divided by
2
12
~2
15
(by option to get the WDT time-out period). The
minimum period of WDT time-out period is about
300ms~600ms. This time-out period may vary with tem-
perature, VDD and process variations. By selection the
WDT option, longer time-out periods can be realized. If
theWDTtime-outisselected2
15
,themaximumtime-out
period is divided by 2
15
~2
16
about 2.1s~4.3s. If the WDT
oscillator is disabled, the WDT clock may still come from
the instruction clock and operate in the same manner
except that in the halt state the WDT may stop counting
and lose its protecting purpose. In this situation the logic
can only be restarted by external logic. If the device op-
erates in a noisy environment, using the on-chip RC os-
cillator (WDT OSC) is strongly recommended, since the
HALT will stop the system clock.
The WDT overflow under normal operation initializes a
chip reset and sets the status bit TO . In the HALT
mode, the overflow initializes a warm reset , and only
the PC and SP are reset to zero. To clear the contents of
the WDT, there are three methods to be adopted, i.e.,
external reset (a low level to RES), software instruction,
and a HALT instruction. There are two types of soft-
ware instructions; CLR WDT and the other set
CLR
WDT1 and CLR WDT2 . Of these two types of instruc-
tion, only one type of instruction can be active at a time
depending on the options
CLR WDT times selection
option. If the CLR WDT is selected (i.e., CLR WDT
times equal one), any execution of the CLR WDT in-
struction clears the WDT. In the case that CLR WDT1
and CLR WDT2 are chosen (i.e., CLR WDT times
equal two), these two instructions have to be executed
to clear the WDT; otherwise, the WDT may reset the
chip due to time-out.
Multi-function Timer
The HT46R64/HT46C64 provides a multi-function timer
for the WDT, time base and RTC but with different
time-out periods. The multi-function timer consists of an
8-stage divider and a 7-bit prescaler, with the clock
source coming from the WDT OSC or RTC OSC or the
instruction clock (i.e., system clock divided by 4). The
multi-function timer also provides a selectable fre-
quency signal (ranges from f
S
/2
2
to f
S
/2
8
) for LCD driver
circuits, and a selectable frequency signal (ranging from
f
S
/2
2
to f
S
/2
9
) for the buzzer output by options. It is rec-
ommended to select a nearly 4kHz signal for the LCD
driver circuits to have proper display.
5
(
/
- & ,
0
- &
- & ,
/
- &
- & ,
- &
- & ,
- &
#
(
6
-
7
'
(
6
'
8 9
1 0 4 8 9
)
)
&
'
6
& -
4
Watchdog Timer
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