7540 datasheet(305/366 Pages) RENESAS

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3-83

REJ09B0018-0200Z

Rev.2.00

Jun 21, 2004

7540 Group

APPENDIX

3.3 Notes on use

3.3.11 Notes on oscillation stop detection circuit

Notes on using oscillation stop detection circuit are described below.

(1) Note on on-chip oscillator

➀ The 7540 Group starts operation by the on-chip oscillator.

➁ On-chip oscillator operation

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.

(2) Notes on oscillation circuit stop detection circuit

➀ When the stop mode is used, set the oscillation stop detection function to “invalid”.

➁ When f(XIN) oscillation is stopped, set the oscillation stop detection function to “invalid”.

➂ The oscillation stop detection circuit is not included in the emulator MCU “M37540RSS”.

(3) Notes on stop mode

➀ When the stop mode is used, set the oscillation stop detection function to “invalid”.

➁ When the stop mode is used, set “0” (STP instruction enabled) to the STP instruction disable bit

of the watchdog timer control register.

➂ Timer 1 can be used to set the oscillation stabilizing time after release of the STP instruction. The

oscillation stabilizing time after release of STP instruction can be selected from “set automatically”/

“not set automatically” by the oscillation stabilizing time set bit after release of the STP instruction

of MISRG. When “0” is set to this bit, “0116” is set to timer 1 and “FF16” is set to prescaler 1

automatically. When “1” is set to this bit, nothing is set to timer 1 and prescaler 1. Therefore, set

the wait time according to the oscillation stabilizing time of the oscillation. Also, when timer 1 is

used, set values again to timer 1 and prescaler 1 after system is returned from the stop mode.

➃ The STP instruction cannot be used during CPU is operating by the on-chip oscillator.

➄ When the stop mode is used, stop the on-chip oscillator oscillation.

➅ Do not execute the STP instruction during the A/D conversion.

(4) Note on wait mode

➀ When the wait mode is used, stop the clock except the operation clock source.

(5) Notes on state transition

➀ When the operation clock source is f(XIN), the CPU clock division ratio can be selected from the

following;

• f(XIN)/2 (high-speed mode)

• f(XIN)/8 (middle-speed mode)

• f(XIN) (double-speed mode)

The double-speed mode can be used only at ceramic oscillation.

Do not use the mode at RC oscillation.

➁ Stabilize the f(XIN) oscillation to change the operation clock source from the on-chip oscillator to f(XIN).

7540 Datasheet(PDF) 305 Page - Renesas Technology Corp

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