R8C datasheet(38/199 Pages) RENESAS

38 / 199 page

R8C/10 Group

Rev.1.20 Jan 27, 2006

page 28 of 180

REJ09B0019-0120

6.5 Oscillation Stop Detection Function

The oscillation stop detection function is such that main clock oscillation circuit stop is detected. The

oscillation stop detection function can be enabled and disabled by the OCD1 to OCD0 bits in the OCD

Table 6.4 lists the specifications of the oscillation stop detection function.

Where the main clock corresponds to the CPU clock source and the OCD1 to OCD0 bits are “112”

(oscillation stop detection function enabled), the system is placed in the following state if the main clock

comes to a halt:

• The on-chip oscillator starts oscillation, and the on-chip oscillator clock becomes the clock source for

CPU clock and peripheral functions in place of the main clock

• OCD register OCD2 bit = 1 (selecting on-chip oscillator clock)

• OCD register OCD3 bit = 1 (main clock stopped)

• CM1 register CM14 bit = 0 (on-chip oscillator oscillating)

• Oscillation stop detection interrupt request occurs

Table 6.4 Oscillation Stop Detection Function Specifications

Item

Specification

Oscillation stop detectable clock and

f(XIN)

≥ 2 MHz

frequency bandwidth

Enabling condition for oscillation stop

Set OCD1 to OCD0 bits to “112” (oscillation stop detection

detection function

function enabled)

Operation at oscillation stop detection

Oscillation stop detection interrupt occurs

6.5.1 How to Use Oscillation Stop Detection Function

• The oscillation stop detection interrupt shares the vector with the watchdog timer interrupt. If the

oscillation stop detection and watchdog timer interrupts both are used, the interrupt factor must be

determined. Table 6.5 shows to determine the interrupt factor with the oscillation stop detection

interrupt, watchdog timer interrupt and voltage detection interrupt.

• Where the main clock re-oscillated after oscillation stop, the clock source for the CPU clock and

peripheral functions must be switched to the main clock in the program.

Figure 6.6 shows the procedure for switching the clock source from the on-chip oscillator to the main

clock.

• To enter wait mode while using the oscillation stop detection function, set the CM02 bit to “0” (periph-

eral function clocks not turned off during wait mode).

• Since the oscillation stop detection function is provided in preparation for main clock stop due to

external factors, set the OCD1 to OCD0 bits to “002” (oscillation stop detection function disabled)

where the main clock is stopped or oscillated in the program, that is where the stop mode is selected

or the CM05 bit is altered.

• This function cannot be used when the main clock frequency is below 2 MHz. Set the OCD1 to OCD0

bits to “002” (oscillation stop detection function disabled).

6.5 Oscillation Stop Detection Function

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