ST10F276 datasheet(204/229 Pages) STMICROELECTRONICS

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Electrical characteristics

ST10F276

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Figure 56.

External clock drive XTAL1

Note:

When Direct Drive is selected, an external clock source can be used to drive XTAL1. The

maximum frequency of the external clock source depends on the duty cycle: When 64 MHz

is used, 50% duty cycle is granted (low phase = high phase = 7.8ns); when for instance

32 MHz is used, a 25% duty cycle can be accepted (minimum phase, high or low, again

equal to 7.8ns).

23.8.16

Memory cycle variables

The tables below use three variables which are derived from the BUSCONx registers and

represent the special characteristics of the programmed memory cycle. The following table

describes how these variables are computed.

Table 102.

External clock drive timing

Symbol

Parameter

Direct drive

fCPU = fXTAL

Direct drive with

prescaler

fCPU = fXTAL / 2

PLL usage

fCPU = fXTAL x F

Unit

Min.

Max.

Min.

Max.

Min.

Max.

tOSCSR

XTAL1 period(1) (2)

The minimum value for the XTAL1 signal period is considered as the theoretical minimum. The real

minimum value depends on the duty cycle of the input clock signal.

4-12 MHz is the input frequency range when using an external clock source. 64 MHz can be applied with

an external clock source only when Direct Drive mode is selected: In this case, the oscillator amplifier is

bypassed so it does not limit the input frequency.

15.625

–

83.3

250

83.3

250

t1 SR

High time(3)

The input clock signal must reach the defined levels VIL2 and VIH2.

–3

–6–

t2 SR

Low time(3)

t3 SR

Rise time(3)

–2–

2–2

t4 SR

Fall time(3)

VIL2

tOSC

VIH2

Table 103.

Memory cycle variables

Symbol

Description

Values

ALE extension

TCL x [ALECTL]

Memory cycle time wait states

2TCL x (15 - [MCTC])

Memory tri-state time

2TCL x (1 - [MTTC])

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