ST92141 datasheet(73/179 Pages) STMICROELECTRONICS

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ST92141 - RESET AND CLOCK CONTROL UNIT (RCCU)

5.5 OSCILLATOR CHARACTERISTICS

The on-chip oscillator circuit uses an inverting gate

circuit with tri-state output.

Notes:

Owing to the Q factor required, Ceramic

Resonators may not provide a reliable oscillator

source.

OSCOUT must not be directly used to drive exter-

nal circuits.

When the oscillator is stopped, OSCOUT goes

high impedance.

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.

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 34. Crystal Oscillator

Table 17. Crystal Specification (5V)

Legend:

CL1, CL2: Maximum Total Capacitances on pins OSCIN

and OSCOUT (the value includes the external capaci-

tance tied to the pin CL1 and CL2 plus the parasitic capac-

itance of the board and of the device).

Note: The tables are relative to the fundamental quartz

crystal only (not ceramic resonator).

Figure 35. Internal Oscillator Schematic

Figure 36. External Clock

OSCIN

OSCOUT

CL1

CL2

ST9

CRYSTAL CLOCK

VR02116A

1M*

*Recommended for oscillator stability

Rs max

(ohm)

CL1=CL2=

56pF

CL1=CL2=

47pF

CL1=CL2=

22pF

Freq.=

3 MHz

270

350

850

Freq.=

4 MHz

150

200

510

Freq.=

5 MHz

110

120

340

VR02086A

HALT

OSCIN

OSCOUT

RIN

ROUT

OSCIN

OSCOUT

CLOCK

INPUT

EXTERNAL CLOCK

VR02116B

ST9

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