ST62P08C ST Microelectronics, ST62P08C Datasheet - Page 19

• Manufacturer Part Number: ST62P08C
• Description: (ST62P08C - ST62P20C) 8-BIT MCU
• Manufacturer: ST Microelectronics

5 CLOCKS, SUPPLY AND RESET
5.1 CLOCK SYSTEM
The main oscillator of the MCU can be driven by
any of these clock sources:
– external clock signal
– external AT-cut parallel-resonant crystal
– external ceramic resonator
– external RC network (R
In addition, an on-chip Low Frequency Auxiliary
Oscillator (LFAO) is available as a back-up clock
system or to reduce power consumption.
An optional Oscillator Safeguard (OSG) filters
spikes from the oscillator lines, and switches to the
LFAO backup oscillator in the event of main oscil-
lator failure. It also automatically limits the internal
clock frequency (f
to guarantee correct operation. These functions
are illustrated in Figure 10, and Figure 11.
Figure 9. Clock Circuit Block Diagram
OSCILLATOR
MAIN
INT
) as a function of V
f
OSG ENABLE OPTION BIT (See OPTION BYTE SECTION)
OSC
NET
).
OSCILLATOR SAFEGU ARD (OSG)
filtering
LFAO
OSG
DD
, in order
(ADCR REGISTER )
OSCOFF BIT
Table 6 illustrates various possible oscillator con-
figurations using an external crystal or ceramic
resonator, an external clock input, an external re-
sistor (R
the LFAO.
For more details on configuring the clock options,
refer to the Option Bytes section of this document.
The internal MCU clock frequency (f
by 12 to drive the Timer, the Watchdog timer and
the A/D converter (if available), and by 13 to drive
the CPU core, as shown in Figure 9.
With an 8 MHz oscillator, the fastest CPU cycle is
therefore 1.625 s.
A CPU 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 CPU cycles for execution.
* Depending on device. See device summary on page 1.
0
1
ST6208C/ST6209C/ST6210C/ST6220C
NET
*
), or the lowest cost solution using only
f
INT
: 12
: 13
CORE
8-BIT TIMER
WATCHDOG
ADC
INT
*
) is divided
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1