st62t65b STMicroelectronics, st62t65b Datasheet - Page 18

• Manufacturer Part Number: st62t65b
• Description: 8-bit Otp/eprom Mcus With A/d Converter, Auto-reload Timer, Eeprom And Spi
• Manufacturer: STMicroelectronics

18
ST62T55B ST62T65B/E65B
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
8 illustrates various possible oscillator configura-
tions using an external crystal or ceramic resonator,
an external clock input, an external resistor (R
C
12 to 22 pF for an oscillator frequency in the 4-8 MHz
range.
A programmable divider is provided in order to adjust
the internal clock of the MCU to the best power con-
sumption and performance trade-off.
The internal MCU clock frequency (f
rectly the AR TIMER while it is divided 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 9.
With an 8MHz oscillator frequency, the fastest ma-
chine cycle is therefore 1.625 s.
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 CRYSTAL/
RESONATOR option isselected,it mustbeusedwith
a quartz crystal, a ceramic resonator or an external
signal provided on the OSCinpin. When theRCNET-
WORK option is selected, the system clock is gen-
erated by an external resistor.
18/74
L1
NET
an C
).
L2
should have a capacitance in the range
INT
) drives di-
NET
).
Figure 8. Oscillator Configurations
C
L1n
CRYSTAL/RES ONATOR CLOCK
CRYSTA L/RESONATOR option
CRYSTAL /RESONATOR option
OSC
RC NETWORK option
EXTE RNAL CLOCK
OSC
OSC
NC
RC NETWORK
in
ST6xxx
in
in
ST6xxx
ST6xxx
OSC
OSC
OSC
NC
out
out
out
R
C
NET
L2