MC68340 datasheet(389/441 Pages) FREESCALE

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10-2

MC68340 USER’S MANUAL

MOTOROLA

MC68340

XTAL

EXTAL

20 M

4.7 pF

10 pF

330 k

32.768 kHz

Figure 10-2. Sample Crystal Circuit

The circuit shown in Figure 10-3 is the typical circuit recommended by Statek Corporation,

for 32768 kHz crystal, part number CX-IV. It is recommended to start with these values,

but parameter values may need to be adjusted to compensate for variables in layout.

MC68340

XTAL

EXTAL

22 M

10 pF

20 pF

470 k

32.768 kHz

Figure 10-3. Statek Corporation Crystal Circuit

A separate power pin (VCCSYN) is used to allow the clock circuits to operate with the rest

of the device powered down and to provide increased noise immunity for the clock circuits.

The source for VCCSYN should be a quiet power supply, and external bypass capacitors

(see Figure 10-4) should be placed as close as possible to the VCCSYN pin to ensure a

stable operating frequency.

Additionally, the PLL requires that an external low-leakage filter capacitor, typically in the

range of 0.01 to 0.1

µF, be connected between the XFC and VCCSYN pins. The XFC

capacitor should provide 50-M

Ω insulation but should not be electrolytic. For external

clock mode without PLL, the XFC pin can be left open. Smaller values of the external filter

capacitor provide a faster response time for the PLL, and larger values provide greater

frequency stability. Figure 10-4 depicts examples of both an external filter capacitor and

bypass capacitors for VCCSYN.

Freescale Semiconductor, Inc.

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MC68340 Datasheet(PDF) 389 Page - Freescale Semiconductor, Inc