ht82j31a Holtek Semiconductor Inc., ht82j31a Datasheet - Page 24

• Manufacturer Part Number: ht82j31a
• Description: 16 Channel A/d Mcu With Spi Interface
• Manufacturer: Holtek Semiconductor Inc.

Oscillator
Various oscillator options offer the user a wide range of
functions according to their various application require-
ments. Four 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.
System Clock Configurations
There are four methods of generating the system clock,
using an external crystal/ceramic oscillator, an external
RC network, an internal RC clock source and a com-
bined internal RC clock source and Real Time Clock.
One of these four methods must be selected using the
configuration options.
System Crystal/Ceramic Oscillator
After selecting the correct configuration option, for most
crystal oscillator configurations, the simple connection
of a crystal across OSC1 and OSC2 will create the nec-
essary phase shift and feedback for oscillation. How-
ever, to ensure oscillation, it is recommended that two
small value capacitors and a resistor, the values of
which are shown in the table, should be connected as
shown in the diagram.
The following table shows the C1, C2 and R1 values ac-
cording different crystal values.
Note:
Rev. 1.00
4MHz Crystal
4MHz Resonator (3 pins)
4MHz Resonator (2 pins)
3.58MHz Crystal
3.58MHz Resonator (2 pins)
2MHz Crystal & Resonator (2 pins)
1MHz Crystal
480kHz Resonator
455kHz Resonator
429kHz Resonator
Crystal or Resonator
The resistance and capacitance for reset circuit
should be designed in such a way as to ensure
that the V
operating voltage range before bringing RES to
high.
nected to the RES pin as short as possible, to
avoid noise interface.
* Make the length of the wiring, which is con-
DD
is stable and remains within a valid
C1, C2
300pF
300pF
300pF
10pF
25pF
25pF
35pF
0pF
0pF
0pF
9.1k
10k
12k
12k
10k
10k
10k
27k
10k
10k
R1
24
External System RC Oscillator
Using the external system RC oscillator requires that a
resistor, with a value between 47k and 750k , is con-
nected between OSC1 and VDD, and a 470pF capacitor
is connected to ground. Although this is a cost effective
oscillator configuration, the oscillation frequency can
vary with VDD, temperature and process variations and
is therefore not suitable for applications where timing is
critical or where accurate oscillator frequencies are re-
quired. For the value of the external resistor ROSC refer
to the Appendix section for typical RC Oscillator vs.
Temperature and VDD characteristics graphics.
Watchdog Timer Oscillator
The WDT oscillator is a fully self-contained free running
on-chip RC oscillator with a typical period of 65 s 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.
Power Down Mode and Wake-up
Power Down Mode
All of the Holtek microcontrollers have the ability to enter
a Power Down Mode. When the device enters this
mode, the normal operating current, will be reduced to
an extremely low standby current level. This occurs be-
cause when the device enters the Power Down Mode,
the system oscillator is stopped which reduces the
power consumption to extremely low levels, however,
as the device maintains its present internal condition, it
can be woken up at a later stage and continue running,
without requiring a full reset. This feature is extremely
important in application areas where the microcontroller
must have its power supply constantly maintained to
keep the device in a known condition but where the
power supply capacity is limited such as in battery appli-
cations.
Entering the Power Down Mode
There is only one way for the device to enter the Power
Down Mode and that is to execute the HALT instruc-
tion in the application program. When this instruction is
executed, the following will occur:
The system oscillator will stop running and the appli-
cation program will stop at the HALT instruction.
September 19, 2007
HT82J31A