DSP56374 View Datasheet(PDF) - Motorola => Freescale

Part Name

Description

Manufacturer

DSP56374

24-Bit Audio Digital Signal Processor

Motorola => Freescale 

External Clock Operation

10 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.

Suggested component values:

fosc = 24.576 MHz

R = 1 M ±10%

C (EXTAL)= 18 pF

C (XTAL) = 47 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

• drive level of 10 µW

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.

EXTAL

VIL

ETH

6

ETL

7

8

ETC

VIH

Midpoint

Note: The midpoint is 0.5 (VIH + VIL).

Figure 2. External Clock Timing

Table 19. Clock Operation

No.

Characteristics

6 EXTAL input high 1

(40% to 60% duty cycle)

7 EXTAL input low1

(40% to 60% duty cycle)

8 EXTAL cycle time

• With PLL disabled

• With PLL enabled

Symbol

Min

Eth

3.33

Etl

3.33

Etc

6.67

50

Max

Units

50

ns

50

ns

inf

ns

200

Freescale Semiconductor

PRELIMINARY

29

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