ST92185B datasheet(58/178 Pages) STMICROELECTRONICS

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ST92185B - RESET AND CLOCK CONTROL UNIT (RCCU)

4.3 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.

The oscillator can not support quartz crystal or ce-

ramic working at the third harmonic without exter-

nal tank circuits.

OSCOUT must not be used to drive external cir-

cuits.

Halt mode is set by means of the HALT instruction.

In this mode the parallel resistor, R, is disconnect-

ed and the oscillator is disabled. This forces the in-

ternal clock 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.

When an HALT instruction is executed, the main

crystal oscillator is stoped and any spurious clock

are ignored. Other analog systems such as the on-

chip line PLL or the whole Video chain (Sync Ex-

traction) must be stopped separately by the soft-

ware as they will induce static consumption.

Table 8. Oscillator Transconductance

Figure 30. Crystal Oscillator

Note: Depending on the application it may be bet-

ter not to implement CL1

Figure 31. Internal Oscillator Schematic

Figure 32. External Clock

Min

Typ

Max

mA/V

0.77

1.5

2.4

OSCIN

OSCOUT

CL1

CL2

ST9

CRYSTAL CLOCK

VR02116A

VR02086A

HALT

OSCIN

OSCOUT

RIN

ROUT

OSCIN

OSCOUT

CLOCK

INPUT

EXTERNAL CLOCK

VR02116B

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