HT48RA0-5 Datasheet, PDF (9/38 Pages) Holtek Semiconductor Inc – Remote Type 8-Bit OTP MCU

HT48RA0-5
In addition, on executing a subroutine call, the status
register will not be automatically pushed onto the stack.
If the contents of the status are important and if the sub-
routine can corrupt the status register, precautions must
be taken to save it properly.
Oscillator Configuration
In this device there are two methods of generating the
system clock, one external crystal oscillator and one in-
ternal RC oscillator.
· External Crystal/Resonator Oscillator - HXT
The External Crystal/Ceramic System Oscillator is
one of the system oscillator choices, which is selected
via a configuration option. For the crystal oscillator
configuration, the connection of a crystal across
OSC1 and OSC2 will create the necessary phase shift
and feedback for oscillation. Two external capacitors
may be required to be connected as shown. However,
the feedback resistor named Rf shown in the following
diagram for the crystal oscillator to oscillate properly
can be selected as either an internally or externally
connected type via a configuration option. When the
external connection type of the feedback resistor is
selected, the recommended value of the external con-
nected feedback resistor ranges from 300kW to
500kW. Using a ceramic resonator will usually require
two small value capacitors, C1 and C2, to be con-
nected as shown for oscillation to occur. The values of
C1 and C2 should be selected in consultation with the
crystal or resonator manufacturer¢s specification.
C1
O SC1
In te r n a l
O s c illa to r
C ir c u it
Rp
Rf
Crystal Oscillator C1 and C2 Values
Crystal Frequency
C1
C2
4MHz
8pF
10pF
Note: C1 and C2 values are for guidance only.
Crystal Recommended Capacitor Values
· Internal RC Oscillator - HIRC
The internal RC oscillator is a fully integrated system
oscillator requiring no external components. The inter-
nal RC oscillator has a fixed frequency of 4095kHz.
Device trimming during the manufacturing process
and the inclusion of internal frequency compensation
circuits are used to ensure that the influence of the
power supply voltage, temperature and process varia-
tions on the oscillation frequency are minimised. As a
result, at a power supply ranging from 1.8V to 3.6V
and in a temperature range from -20°C to 50°C de-
grees, the fixed oscillation frequency of 4095kHz will
have a tolerance within 2%. Note that if this internal
system clock option is selected, as it requires no ex-
ternal pins for its operation, I/O pins PB5 and PB6 are
free for use as normal I/O pins.
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 . C 1 a n d C 2 a r e 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 - HXT
Rev.1.10
9
June 10, 2010