ST72681SLASHR21 datasheet(19/32 Pages) STMICROELECTRONICS

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ST72681

Electrical characteristics

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7.5

Clock and timing characteristics

Subject to general operating conditions for VDD33, fOSC, and TA.

7.5.1

General timings

7.5.2

Crystal oscillator

The ST72681 internal clock is supplied from a crystal oscillator. All the information given in

this paragraph are based on characterization results with specified typical external

components. In the application the load capacitors have to be placed as close as possible to

the oscillator pins in order to minimize output distortion and start-up stabilization time. Refer

to the crystal manufacturer for more details (frequency, package, accuracy...).

Figure 7.

Typical application with a crystal oscillator

Depending on the crystal oscillator power dissipation, a serial resistor RsOscout may be added. Refer to the

crystal oscillator manufacturer for more details.

Table 13.

General timing characteristics

Symbol

Parameter

Conditions

Min.

Typ. (1)

Data based on typical application software.

Max.

Unit

tc(INST) Instruction cycle time

tCPU

fCPU = 15 MHz

133

200

800

tv(IT)

Interrupt reaction time (2)

tv(IT) = Δtc(INST) + 10

Time measured between interrupt event and interrupt vector fetch.

Δtc(INST) is the number of tCPU cycles

required to finish executing the current instruction.

tCPU

fCPU = 12 MHz

0.666

1.466

µs

Table 14.

Crystal oscillator characteristics

Symbol

Parameter

Conditions

Min.

Typ.

Max.

Unit

fOSC

Oscillator frequency

MHz

CKACC

Total crystal oscillator accuracy abs. value + temp + aging

±60

ppm

αOSC

Crystal oscillator duty cycle (1)

The crystal oscillator duty cycle has to be adjusted through the two CL capacitors. Refer to the crystal

manufacturer for more details.

Table 15.

Typical CL and RS values by crystal oscillator

Supplier

Typical crystal oscillator

CL (pF)

RsOscout (Ω)

NDK

AT51 or AT41

560

OSCOUT

OSCIN

Device

CRYSTAL

RsOscout

(1)

VDDA

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