ST92F120 datasheet(104/324 Pages) STMICROELECTRONICS

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ST92F120 - RESET AND CLOCK CONTROL UNIT (RCCU)

7.5 OSCILLATOR CHARACTERISTICS

The on-chip oscillator circuit uses an inverting gate

circuit with tri-state output.

OSCOUT must not be used to drive external cir-

cuits.

When the oscillator is stopped, OSCOUT goes

high impedance.

In Halt mode, set by means of the HALT instruc-

tion, the parallel resistor, R, is disconnected and

the oscillator is disabled, forcing the internal clock,

CLOCK1, to a high level, and OSCOUT to a high

impedance state.

To exit the HALT condition and restart the oscilla-

tor, an external RESET pulse is required, having a

a minimum duration of 20

µs, as illustrated in Fig-

ure 54.

It should be noted that, if the Watchdog function is

enabled, a HALT instruction will not disable the os-

cillator. This to avoid stopping the Watchdog if a

HALT

code is executed in error. When this occurs,

the CPU will be reset when the Watchdog times

out or when an external reset is applied.

Figure 49. Crystal Oscillator

Table 23. RS Crystal Specification

Legend:

C1, C2: Maximum Total Capacitances on pins OSCIN and

OSCOUT (the value includes the external capacitance

tied to the pin plus the parasitic capacitance of the board

and of the device)

Note: The tables are relative to the fundamental quartz

crystal only (not ceramic resonator).

Figure 50. Internal Oscillator Schematic

Figure 51. External Clock

OSCIN

OSCOUT

ST9

CRYSTAL CLOCK

VR02116A

1 M

Ω *

*Recommended for oscillator stability

C1=C2

Freq.

33pF

22pF

5 MHz

80 ohm

130 ohm

4 MHz

130 ohm

200 ohm

3 MHz

250 ohm

VR02086A

REF

CLOCK

INPUT

BUFFER

OSCIN

OSCOUT

HALT

OSCIN

OSCOUT

CLOCK

INPUT

EXTERNAL CLOCK

VR02116B

ST9

3.3 k

Ω

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