R8C2K datasheet(109/471 Pages) RENESAS

109 / 471 page

R8C/2K Group, R8C/2L Group

10. Clock Generation Circuit

Rev.1.10

Dec 21, 2007

Page 92 of 450

REJ09B0406-0110

10.5

Oscillation Stop Detection Function

The oscillation stop detection function detects the stop of the XIN clock oscillating circuit. The oscillation stop

detection function can be enabled and disabled by the OCD0 bit in the OCD register.

Table 10.5 lists the Specifications of Oscillation Stop Detection Function.

When the XIN clock is the CPU clock source and bits OCD1 to OCD0 are set to 11b, the system is placed in the

following state if the XIN clock stops.

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

• OCD3 bit in OCD register = 1 (XIN clock stops)

• CM14 bit in CM1 register = 0 (low-speed on-chip oscillator oscillates)

• Oscillation stop detection interrupt request is generated.

10.5.1

How to Use Oscillation Stop Detection Function

• The oscillation stop detection interrupt shares a vector with the voltage monitor 1 interrupt, the voltage

monitor 2 interrupt, and the watchdog timer interrupt. When using the oscillation stop detection interrupt and

watchdog timer interrupt, the interrupt source needs to be determined.

Table 10.6 lists the Determining Interrupt Source for Oscillation Stop Detection, Watchdog Timer, Voltage

Monitor 1, and Voltage Monitor 2 Interrupts. Figure 10.15 shows the Example of Determining Interrupt

Source for Oscillation Stop Detection, Watchdog Timer, Voltage Monitor 1, or Voltage Monitor 2 Interrupt.

• When the XIN clock restarts after oscillation stop, switch the XIN clock to the clock source of the CPU clock

and peripheral functions by a program.

Figure 10.14 shows the Procedure for Switching Clock Source from Low-Speed On-Chip Oscillator to XIN

Clock.

• To enter wait mode while using the oscillation stop detection function, set the CM02 bit to 0 (peripheral

function clock does not stop in wait mode).

• Since the oscillation stop detection function is a function for cases where the XIN clock is stopped by an

external cause, set bits OCD1 to OCD0 to 00b when the XIN clock stops or is started by a program, (stop

mode is selected or the CM05 bit is changed).

• This function cannot be used when the XIN clock frequency is 2 MHz or below. In this case, set bits OCD1 to

OCD0 to 00b.

• To use the low-speed on-chip oscillator clock for the CPU clock and clock sources of peripheral functions

after detecting the oscillation stop, set the FRA01 bit in the FRA0 register to 0 (low-speed on-chip oscillator

selected) and bits OCD1 to OCD0 to 11b.

To use the high-speed on-chip oscillator clock for the CPU clock and clock sources of peripheral functions

after detecting the oscillation stop, set the FRA00 bit to 1 (high-speed on-chip oscillator on) and the FRA01

bit to 1 (high-speed on-chip oscillator selected) and then set bits OCD1 to OCD0 to 11b.

Table 10.5

Specifications of Oscillation Stop Detection Function

Item

Specification

Oscillation stop detection clock and

frequency bandwidth

f(XIN)

≥ 2 MHz

Enabled condition for oscillation stop

detection function

Set bits OCD1 to OCD0 to 11b

Operation at oscillation stop detection

Oscillation stop detection interrupt is generated

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