56F8166 datasheet(39/182 Pages) FREESCALE

39 / 182 page

External Clock Operation

56F8366 Technical Data, Rev. 7

Freescale Semiconductor

Preliminary

The crystal and associated components should be mounted as near as possible to the EXTAL and XTAL

pins to minimize output distortion and start-up stabilization time.

Figure 3-2 Connecting to a Crystal Oscillator

Note:

The OCCS_COHL bit must be set to 1 when a crystal oscillator is used. The reset condition on the

OCCS_COHL bit is 0. Please see the COHL bit in the Oscillator Control (OSCTL) register, discussed

in the 56F8300 Peripheral User Manual.

3.2.2

Ceramic Resonator (Default)

It is also possible to drive the internal oscillator with a ceramic resonator, assuming the overall system

design can tolerate the reduced signal integrity. A typical ceramic resonator circuit is shown in Figure 3-3.

Refer to the supplier’s recommendations when selecting a ceramic resonator and associated components.

The resonator and components should be mounted as near as possible to the EXTAL and XTAL pins.

Figure 3-3 Connecting a Ceramic Resonator

Note:

The OCCS_COHL bit must be set to 0 when a ceramic resonator is used. The reset condition on the

OCCS_COHL bit is 0. Please see the COHL bit in the Oscillator Control (OSCTL) register, discussed

in the 56F8300 Peripheral User Manual.

Sample External Crystal Parameters:

Rz = 750 KΩ

Note: If the operating temperature range is limited to

below 85oC (105oC junction), then Rz = 10 Meg Ω

CLKMODE = 0

EXTAL XTAL

CL1

CL2

Crystal Frequency = 4 - 8MHz (optimized for 8MHz)

EXTAL XTAL

EXTAL

XTAL

Sample External Ceramic Resonator Parameters:

Rz = 750 KΩ

EXTAL

XTAL

CL1

CL2

Resonator Frequency = 4 - 8MHz (optimized for 8MHz)

3 Terminal

2 Terminal

CLKMODE = 0

56F8166 데이터시트(PDF) 39 Page - Freescale Semiconductor, Inc

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