4501 datasheet(166/212 Pages) RENESAS

166 / 212 page

2.8 Oscillation circuit

2-49

4501 Group

APPLICATION

Rev.2.01

Feb 07, 2005

REJ09B0192-0201

2.8 Oscillation circuit

The 4501 Group has an internal oscillation circuit to produce the clock required for microcomputer operation.

The ceramic resonance and the RC oscillation can be used for the source clock.

After system is released from reset, the 4501 Group starts operation by the clock output from the on-chip

oscillator which is the internal oscillator.

Fig. 2.8.1 Switch to ceramic resonance/RC oscillation

Reset

On-chip oscillator

operation

CMCK instruction

CRCK instruction

• Ceramic resonator valid

• On-chip oscillator stop

• RC oscillation stop

• RC oscillation valid

• On-chip oscillator stop

• Ceramic resonator stop

2.8.1 Oscillation circuit

(1)

f(XIN) clock generating circuit

The ceramic resonator or RC oscillation can

be used for the source oscillation (f(XIN)) of

the MCU.

After system is released from reset, the 4501

Group starts operation by the clock output from

the on-chip oscillator which is the internal

oscillator.

When the ceramic resonator is used, execute

the CMCK instruction. When the RC oscillation

is used, execute the CRCK instruction. The

oscillation circuit by the CMCK or CRCK

instruction can be selected only at once. The

oscillation circuit corresponding to the first

executed one of these two instructions is valid.

Other oscillation circuit and the on-chip

oscillator stop.

Execute the CMCK or the CRCK instruction

in the initial setting routine of program

(executing it in address 0 in page 0 is

recommended). Also, when the CMCK or the

CRCK instruction is not executed in program,

the 4501 Group operates by the on-chip

oscillator.

(2)

On-chip oscillator operation

When the MCU operates by the on-chip

oscillator as the source oscillation (f(XIN))

without using the ceramic resonator or the

RC oscillator, connect XIN pin to VSS and leave

XOUT pin open (Figure 2.8.2).

The clock frequency of the on-chip oscillator

depends on the supply voltage and the

operation temperature range.

Be careful that variable frequencies when

designing application products.

Fig. 2.8.2 Handling of XIN and XOUT when operating

on-chip oscillator

4501

XIN

XOUT

Do not use the CMCK instruction

and CRCK instruction in program.

4501 Datasheet(PDF) 166 Page - Renesas Technology Corp

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