7549 datasheet(52/84 Pages) RENESAS

52 / 84 page

Rev.2.01

Oct 15, 2007

Page 52 of 81

REJ03B0202-0201

7549 Group

• Oscillation stop detection circuit

The oscillation stop detection circuit is used to detect an

oscillation stop when a ceramic resonator or oscillation circuit

stops due to disconnection. To use the oscillation stop detection

circuit, set the low-speed on-chip oscillator to start operating.

The oscillation stop detection circuit is enabled by setting the

XIN oscillation stop detection function active bit to 1. While this

circuit is enabled, the operating status of the XIN oscillation

circuit is monitored using the low-speed on-chip oscillator. If an

oscillation stop is detected, the oscillation stop detection status

bit is set to 1. If the oscillation stop detection reset enable bit is

also set to 1, an internal reset is triggered at oscillation stop

detection.

The XIN oscillation stop detection function active bit and the

oscillation stop detection status bit are not initialized if an

oscillation stop detection reset is triggered and these bits retain

their value of 1. Since these bits are initialized to 0 by an external

reset, an oscillation stop detection reset can be determined by

checking the oscillation stop status bit.

The oscillation stop detection status bit is set to 0 by writing 0 to

the XIN oscillation stop detection function enable bit.

To enable the oscillation detection circuit, first write 0 to the XIN

oscillation stop detection function enable bit and set the

oscillation stop detection status bit to 0. Then set the oscillation

stop function to 1.

The XIN oscillation and external clock input are set as the clocks

for oscill ati o n stop detect ion. Refer t o the el ectrica l

characteristics for the frequencies for oscillation stop detection.

Fig 67. Structure of oscillation stop detection register

•Notes

(1)

Do not execute the transition to “state 2’a” shown in Figure

68 State transition of oscillation stop detection circuit. In

this state, no reset is triggered and the MCU is stopped even

when the XIN oscillation stops.

(2) After an oscillation stop detection reset, if this reset is

enabled while bits XIN oscillation stop detection function

active and oscillation stop detection status are retained, a

reset is triggered again.

(3) The oscillation stop detection status bit is initialized under

the following conditions:

• External reset, power-on reset, low-voltage detection reset,

watchdog timer reset, and reset by the STP instruction

function.

• Write 0 to the XIN oscillation stop detection function active

bit

(4) While the oscillation stop detection function is in active, the

oscillation stop detection status bit may set to 1 when the

watchdog timer underflows or by a reset when the STP

instruction is executed with the STP instruction function

selection bit set to 1.

When an oscillation stop detection reset is triggered,

reconfirm that oscillation is stopped.

(5) The oscillation stop detection circuit is not included in the

emulator MCU “M37549RLSS”.

XIN oscillation stop detection function active bit

0: Detection function inactive

1: Detection function active

Oscillation stop detection reset enable bit

0: Oscillation stop detection reset disabled

1: Oscillation stop detection reset enabled

Oscillation stop detection status bit

0: Oscillation stop not detected

1: Oscillation stop detected

Not used (“0” at reading)

Oscillation stop detection register

(CLKSTP: address 003816, initial value: 0016)

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