ST90R158 datasheet(77/190 Pages) STMICROELECTRONICS

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ST90158 - RESET AND CLOCK CONTROL UNIT (RCCU)

6.5 OSCILLATOR CHARACTERISTICS

The on-chip oscillator circuit uses an inverting gate

circuit with tri-state output.

Notes:

It is recommended to place the quartz or

crystal as close as possible to the ST9 to reduce

the parasitic capacitance. At low temperature,

frost and humidity might prevent a correct start-up

of the oscillator.

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 12ms, as illustrated in Fig-

ure 41

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.

Table 15. Oscillator Transconductance

Figure 37. Crystal Oscillator

Table 16. Crystal Internal Resistance(

Ω) (5V

Op.)

Table 17. Crystal Internal Resistance(

Ω) (3V

Op.)

Legend:

CL1,CL2: Maximum Total Capacitance 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 38. Internal Oscillator Schematic

Figure 39. External Clock

Min

Typ

Max

5V Operation

mA/V

0.77

1.5

2.4

3V Operation

0.42

0.73

1.47

OSCIN

OSCOUT

CL1

CL2

ST9

CRYSTAL CLOCK

Ω

*Recommended for oscillator stability

C1=C2

Freq.

56pF

47pF

33pF

22pF

5 Mhz

110

120

210

340

4 Mhz

150

200

330

510

3 Mhz

270

350

560

850

C1=C2

Freq.

56pF

47pF

33pF

22pF

5 Mhz

120

4 Mhz

125

195

3 Mhz

100

135

220

350

HALT

OSCIN

OSCOUT

RIN

ROUT

OSCIN

OSCOUT

CLOCK

INPUT

EXTERNAL CLOCK

ST9

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