DSP56300FMSLASHAD datasheet(30/64 Pages) FREESCALE

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DSP56374 Data Sheet, Rev. 4.2

External Clock Operation

Freescale Semiconductor

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 low2

(40% to 60% duty cycle)

Etl

3.33

EXTAL cycle time

• With PLL disabled

• With PLL enabled

Etc

6.67

inf

200

Instruction cycle time= ICYC = TC

• With PLL disabled

• With PLL enabled

Icyc

6.67

inf

13.33

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) 30 Page - Freescale Semiconductor, Inc

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