DSP56311 View Datasheet(PDF) - Freescale Semiconductor

Part Name

Description

Manufacturer

DSP56311

24-Bit Digital Signal Processor

Freescale Semiconductor 

AC Electrical Characteristics

2.4.2 External Clock Operation

The DSP56311 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; examples are

shown in Figure 2-1.

EXTAL

XTAL

R

C

XTAL1

C

Fundamental Frequency

Crystal Oscillator

Note: Make sure that in

the PCTL Register:

• XTLD (bit 16) = 0

• If fOSC > 200 kHz,

XTLR (bit 15) = 0

Suggested Component Values:

fOSC = 4 MHz

R = 680 kΩ ± 10%

C = 56 pF ± 20%

fOSC = 20 MHz

R = 680 kΩ ± 10%

C = 22 pF ± 20%

Calculations were done for a 4/20 MHz crystal

with the following parameters:

• CLof 30/20 pF,

• C0 of 7/6 pF,

• series resistance of 100/20 Ω, and

• drive level of 2 mW.

Figure 2-1. Crystal Oscillator Circuits

If an externally-supplied square wave voltage source is used, disable the internal oscillator circuit during bootup by

setting XTLD (PCTL Register bit 16 = 1—see the DSP56311 User’s Manual). The external square wave source

connects to EXTAL; XTAL is not physically connected to the board or socket. Figure 2-2 shows the relationship

between the EXTAL input and the internal clock and CLKOUT.

EXTAL

Midpoint

VIHX

VILX ETH

2

5

CLKOUT with

PLL disabled

ETL

3

4

ETC

Note:

The midpoint is

0.5 (VIHX + VILX).

5

7

CLKOUT with

PLL enabled

6a

6b

7

Figure 2-2. External Clock Timing

DSP56311 Technical Data, Rev. 8

Freescale Semiconductor

2-5

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