Motorola MC68HC05RC16, MC68HC05RC8 manual 24

General Description

1.5.3 OSC1 and OSC2

These pins provide control input for an on-chip clock oscillator circuit. A crystal, a ceramic resonator, or an external signal connects to these pins to provide a system clock. The oscillator frequency is two times the internal bus rate.

Figure 1-5shows the recommended circuit when using a crystal. The crystal and components should be mounted as close as possible to the input pins to minimize output distortion and startup stabilization time.

A ceramic resonator may be used in place of the crystal in cost-sensitive applications. Figure 1-5(a) shows the recommended circuit for using a ceramic resonator. The manufacturer of the particular ceramic resonator being considered should be consulted for specific information.

An external clock should be applied to the OSC1 input with the OSC2 pin not connected (see Figure 1-5(b)). This setup can be used if the user does not want to run the CPU with a crystal.

		MCU				MCU
	OSC1		OSC2		OSC1	OSC2
		10 MΩ						UNCONNECTED
30 pF							< EXTERNAL CLOCK
				30 pF

(a) Crystal/Ceramic Resonator	(b) External Clock Source
Oscillator Connections	Connections

Figure 1-5. Oscillator Connections

General Release Specification		MC68HC05RC16 — Rev. 3.0
24	General Description	MOTOROLA