DSP56300FMSLASHAD datasheet(29/128 Pages) MOTOROLA

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External Clock Operation

Freescale Semiconductor

PRELIMINARY

External Clock Operation

The DSP56374 system clock is derived from the on-chip oscillator or is externally supplied. To use the on-chip oscillator, connect

a crystal and associated resistor/capacitor components to EXTAL and XTAL; an example is shown below.

If the DSP56374 system clock is an externally supplied square wave voltage source, it is connected to EXTAL (Figure 2). When

the external square wave source connects to EXTAL, the XTAL pin is not used.

Figure 2.

External Clock Timing

Table 19. Clock Operation

No.

Characteristics

Symbol

Min

Max

Units

EXTAL input high 1

(40% to 60% duty cycle)

Eth

3.33

EXTAL input low1

(40% to 60% duty cycle)

Etl

3.33

EXTAL cycle time

• With PLL disabled

• With PLL enabled

Etc

6.67

inf

200

Suggested component values:

fosc = 24.576 MHz

R = 1 M ±10%

C (EXTAL)= 18 pF

Calculations are for a 12 - 49 MHz crystal with the following parameters:

• shunt capacitance (C0) of 10 pF - 12 pF

• series resistance 40 Ohm

C (XTAL) = 47 pF

• drive level of 10

µW

EXTAL

VIL

VIH

Midpoint

Note:

The midpoint is 0.5 (VIH + VIL).

ETH

ETL

ETC

DSP56300FM/AD Datasheet(PDF) 29 Page - Motorola, Inc

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