st62t62cmae STMicroelectronics, st62t62cmae Datasheet - Page 17

• Manufacturer Part Number: st62t62cmae
• Description: 8-bit Otp/eprom/fastrom Mcus With A/d Converter, Safe Reset, Auto-reload Timer And Eeprom
• Manufacturer: STMicroelectronics

3 CLOCKS, RESET, INTERRUPTS AND POWER SAVING MODES
3.1 CLOCK SYSTEM
The MCU features a Main Oscillator which can be
driven by an external clock, or used in conjunction
with an AT-cut parallel resonant crystal or a suita-
ble ceramic resonator, or with an external resistor
(R
cillator (LFAO) can be switched in for security rea-
sons, to reduce power consumption, or to offer the
benefits of a back-up clock system.
The Oscillator Safeguard (OSG) option filters
spikes from the oscillator lines, provides access to
the LFAO to provide a backup oscillator in the
event of main oscillator failure and also automati-
cally limits the internal clock frequency (f
function of V
ation. These functions are illustrated in
Figure
Figure 8.
figurations using an external crystal or ceramic res-
onator, an external clock input, an external resistor
(R
LFAO. C
range 12 t o 22 pF for an oscillator frequency in the
4-8 MHz range.
The internal MCU clock frequency (f
by 12 to drive the Timer, the A/D converter and the
Watchdog timer, and by 13 to drive the CPU core,
as may be seen in
With an 8 MHz oscillator frequency, the fastest ma-
chine cycle is therefore 1.625µs.
A machine cycle is the smallest unit of time needed
to execute any operation (for instance, to increment
the Program Counter). An instruction may require
two, four, or five machine cycles for execution.
3.1.1 Main Oscillator
The oscillator configuration may be specified by se-
lecting the appropriate option. When the CRYS-
TAL/RESONATOR option is selected, it must be
used with a quartz crystal, a ceramic resonator or an
external signal provided on the OSCin pin. When the
RC NETWORK option is selected, the system clock
is generated by an external resistor.
The main oscillator can be turned off (when the
OSG ENABLED option is selected) by setting the
OSCOFF bit of the ADC Control Register. The
Low Frequency Auxiliary Oscillator is automatical-
ly started.
NET
NET
). In addition, a Low Frequency Auxiliary Os-
), or the lowest cost solution using only the
10.,
L1
illustrates various possible oscillator con-
an C
Figure 11.
DD
, in order to guarantee correct oper-
L2
should have a capacitance in the
Figure
and
11..
Figure
12..
INT
) is divided
Figure
INT
) as a
9.,
Figure 8. Oscillator Configurations
ST62T52CM-Auto ST62T62CM-Auto
C
L1n
CRYSTAL/RESONATOR CLOCK
CRYSTAL/RESONATOR option
CRYSTAL/RESONATOR option
CRYSTAL/RESONATOR option
OSG ENABLED option
INTEGRATED CLOCK
RC NETWORK option
OSC
OSC
EXTERNAL CLOCK
OSC
OSC
NC
RC NETWORK
in
in
in
ST6xxx
ST6xxx
ST6xxx
in
ST6xxx
OSC
OSC
OSC
OSC
NC
NC
out
out
out
out
R
C
NET
L2
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