7540 datasheet(213/366 Pages) RENESAS

213 / 366 page

2-137

REJ09B0018-0200Z

Rev.2.00

Jun 21, 2004

7540 Group

APPLICATION

2.9 Reset

2.9.3 Application example of on-chip oscillator

The on-chip oscillator is the oscillation circuit which is equipped with the 7540 Group. External circuits can

be eliminated by using this oscillator as the operation clock or by using this oscillator with a ceramic or

RC oscillation circuit. When this oscillator is used as the operation clock, all peripheral functions can be

used. In this section, the setting method and application example are explained.

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

(1) Setting method

Figure 2.9.5 shows the setting method when the on-chip oscillator is used as the operation clock.

Fig. 2.9.5 Setting method when the on-chip oscillator is used as the operation clock

Process 1: Enable on-chip oscillator oscillation.

b7b0

CPU mode register (CPUM) [Address 3B16]

on-chip oscillatior oscillation enabled

Process 2: Set the operation clock to on-chip oscillator.

b7b0

Applied from on-chip oscillator

Process 3: When f(XIN) is not used, stop f(XIN).

b7b0

Ceramic or RC oscillation stop

CPU mode register (CPUM) [Address 3B16]

(2) Example of control procedure

Outline: The frequency of the on-chip oscillator is measured, and an error by the power source

voltage or temperature is confirmed.

Specifications: • The f(XIN) = 4 MHz is divided by timer Z and 10 ms is detected. The on-chip

oscillator is divided by timer Y.

• The count value of timer Y is read out in the timer Z interrupt processing routine

which occurs every 10 ms, and an error from f(XIN) is confirmed.

Figure 2.9.6 shows an example of control procedure.

7540 Datasheet(PDF) 213 Page - Renesas Technology Corp