HT83F02 Datasheet, PDF (41/64 Pages) Holtek Semiconductor Inc – External Voice Memory Flash MCU

HT83F02
Oscillator
Various oscillator options offer the user a wide range of
functions according to their various application require-
ments. Three types of system clocks can be selected
while various clock source options for the Watchdog
Timer are provided for maximum flexibility. All oscillator
options are selected through the configuration options.
The three methods of generating the system clock are:
· External crystal/resonator oscillator
· External RC oscillator
· Internal RC oscillator
One of these three methods must be selected using the
configuration options.
More information regarding the oscillator is located in
Application Note HA0075E on the Holtek website.
External Crystal/Resonator Oscillator
The simple connection of a crystal across OSC1 and
OSC2 will create the necessary phase shift and feed-
back for oscillation, and will normally not require exter-
nal capacitors. However, for some crystals and most
resonator types, to ensure oscillation and accurate fre-
quency generation, it may be necessary to add two
small value external capacitors, C1 and C2. The exact
values of C1 and C2 should be selected in consultation
with the crystal or resonator manufacturer¢s specifica-
tion. The external parallel feedback resistor, Rp, is nor-
mally not required but in some cases may be needed to
assist with oscillation start up.
Internal Ca, Cb, Rf Typical Values @ 5V, 25°C
Ca
Cb
Rf
11~13pF
13~15pF
800kW
Oscillator Internal Component Values
C1
O SC1
In te r n a l
O s c illa to r
Ca
C ir c u it
Rp
Rf
Cb
T o in te r n a l
C2
O SC2
c ir c u its
N o te : 1 . R p is n o r m a lly n o t r e q u ir e d .
2 . A lth o u g h n o t s h o w n O S C 1 /O S C 2 p in s h a v e a p a r a s itic
c a p a c ita n c e o f a r o u n d 7 p F .
Crystal/Resonator Oscillator
External RC Oscillator
Using the external system RC oscillator requires that a
resistor, with a value between 150kW and 300kW, is con-
nected between OSC1 and VSS. The generated system
clock divided by 4 will be provided on OSC2 as an out-
put which can be used for external synchronization pur-
poses. Note that as the OSC2 output is an NMOS
open-drain type, a pull high resistor should be con-
nected if it to be used to monitor the internal frequency.
Although this is a cost effective oscillator configuration,
the oscillation frequency can vary with VDD, tempera-
ture and process variations and is therefore not suitable
for applications where timing is critical or where accu-
rate oscillator frequencies are required. For the value of
the external resistor R_OSC refer to the Holtek website for
typical RC Oscillator vs. Temperature and VDD charac-
teristics graphics. Note that it is the only microcontroller
internal circuitry together with the external resistor, that
determine the frequency of the oscillator. The external
capacitor shown on the diagram does not influence the
frequency of oscillation.
O SC1
R O SC
fS Y S /4 N M O S O p e n D r a in
O SC2
External RC Oscillator
Internal RC Oscillator
The internal RC oscillator is a fully integrated system os-
cillator requiring no external components. The internal
RC oscillator has three fixed frequencies of either
4MHz, 8MHz or 12MHz selected by configuration op-
tions. Device trimming during the manufacturing pro-
cess and the inclusion of internal frequency
compensation circuits are used to ensure that the influ-
ence of the power supply voltage, temperature and pro-
cess variations on the oscillation frequency are
minimised. As a result, at a power supply of either 3.3V
or 5V and at a temperature of 25°C degrees, the fixed
oscillation frequency of 4MHz, 8MHz or 12MHz will have
a tolerance within 2%. Note that if this internal system
clock option is selected, as it requires no external pins
for its operation, I/O pins PC1 and PC2 are free for use
as normal I/O pins.
I/O
O SC1
I/O
O SC2
Internal RC Oscillator -- HIRC
Watchdog Timer Oscillator
The WDT oscillator is a fully self-contained free running
on-chip RC oscillator with a typical period of 65ms at 5V
requiring no external components. When the device en-
ters the Power Down Mode, the system clock will stop
running but the WDT oscillator continues to free-run and
to keep the watchdog active. However, to preserve
power in certain applications the WDT oscillator can be
disabled via a configuration option.
Rev. 1.20
41
November 19, 2010