455A datasheet(63/148 Pages) RENESAS

63 / 148 page

Rev.1.01

Feb 15, 2008

Page 63 of 146

REJ03B0224-0101

455A Group

(1) High-speed on-chip oscillator operation

After system is released from reset, the MCU starts operation by

the clock output from the high-speed on-chip oscillator which is

the internal oscillator.

The clock frequency of the high-speed on-chip oscillator depends

on the supply voltage and the operation temperature range.

Be careful that variable frequencies when designing application

products.

(2) Main clock generating circuit (f(XIN))

After reset release, the ceramic oscillation is valid for the main

clock. Connect the ceramic oscillator and the external circuit to

pins XIN and XOUT at the shortest distance (Figure 61). A

feedback resistor is built in between pins XIN and XOUT.

If the main clock is not used, connect the XIN pin to VSS and

leave the XOUT pin open.

(3) Low-speed on-chip oscillator operation

After system is released from reset, the low-speed on-chip

oscillator turns invalid which is the internal oscillator.

Oscillator operation/stopping and the control of system clock

selection are operated by the register RG and MR.

The clock frequency of the low-speed on-chip oscillator depends

on the supply voltage and the operation temperature range.

Be careful that variable frequencies when designing application

products.

Fig 60. Handling of XIN and XOUT when operating on-

chip oscillator

Fig 61. Ceramic resonator external circuit

455A

XIN

XOUT

455A

XIN

XOUT

CIN

COUT

Note: Externally connect a damping resistor Rd

depending on the oscillation frequency.

(A feedback resistor is built-in.)

Use the resonator manufacturer’s recommended

value because constants such as capacitance

depend on the resonator.

455A Datasheet(PDF) 63 Page - Renesas Technology Corp

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