7549 datasheet(49/73 Pages) RENESAS

49 / 73 page

Rev.2.00

Mar 05, 2007

Page 49 of 70

REJ03B0202-0200

7549 Group

PRELIMINARY

Notice: This is not a final specification.

Some parametric limits are subject to change.

• Oscillation stop detection circuit

The oscillation stop detection circuit is used for reset occurrence

when a ceramic resonator or RC oscillation circuit stops by

disconnection. To use this circuit, set an on-chip oscillator to be

in active.

The oscillation stop detection circuit is in active to set “1” to the

XIN oscillation stop detection function active bit.

When the oscillation stop detection circuit is enabled, the

operation status of the XIN oscillator circuit is monitored using

the low-speed on-chip oscillator, and if oscillation stop is

detected the oscillation stop detection status bit is set to 1. If

additionally the oscillation stop detection reset enable bit is set to

“1”, an internal reset is triggered when the oscillator stops

operating.

The oscillation stop detection status bit is not initialized by an

oscillation stop detection reset and retains its value of 1. Since

the oscillation stop detection status bit is initialized to “0” by an

external reset, it is possible to determine if a reset was due to

oscillation stop detection by checking the oscillation stop

detection status bit.

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

to detect the oscillation stop.

Refer to the electrical characteristics for the frequencies to detect

the oscillation stop.

• Notes on Oscillation Stop Detection Circuit

(1) Do not execute the transition to “state 2'a” shown in Figure

65 because in this “state 2'a”, MCU is stopped without reset

even when XIN oscillation is stopped.

(2) XIN oscillation stop detection function active bit is not

cleared by the oscillation stop detection reset. Accordingly,

the oscillation stop detection circuit is in active when system

is released from internal reset cause of oscillation stop

detection.

(3) Oscillation stop detection status bit is initialized by the

following operation.

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

watchdog timer reset, and reset by STP instruction function

• Write “0” data to the XIN oscillation stop detection

function active bit.

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

emulator MCU “M37549RLSS”.

Fig 64. Structure of oscillation stop detection register

Fig 65. State transition of oscillation stop detection circuit

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)

Notes on switch of clock

(1) Executing the state transition after stabilizing XIN oscillation.

(2) MCU cannot be returned by on-chip oscillator and its operation is stopped since internal reset does not

occur at oscillation stop detected in state 2'a. Accordingly, do not execute the transition to state 2'a.

(3) STP instruction cannot be used when oscillation stop detection circuit is in active.

(4) The same applies when the high-speed on-chip oscillator is set as

φSOURCE. Make sure that the low-speed

on-chip oscillator should also oscillate. When a reset occurs, the high-speed on-chip oscillator stops.

Reset state 1

Oscillation stop detection reset disabled

When oscillation stop is detected;

CLKSTP2 is set to “1”.

Internal RESET does not occur.

= 02

= 12

CLKSTP0 = 02

(CLKSTP2 is set to “0”.)

CLKSTP 0 = 12

(Note 1)

Oscillation stop is detected

(internal reset)

Reset state 2

External reset (RESET=“L”)

⋅ Power-on reset

⋅ Low voltage detection reset

⋅ Watchdog timer reset

⋅ Reset by STP instruction function

Return from oscillation stop detection reset

CLKSTP2 is set to “1”.

So, return from oscillation stop reset can be

confirmed.

CLKSTP1= 02

CLKSTP1 = 02

(CLKSTP2 is

set to “0”.)

CLKM54 = 102

CLKM54 = 002

(Note 1)

Prohibitive state

MCU stops when oscillation stops

occurs.

State 3'a

State 2'b

State 3'b

State 3'c

Oscillation stop detection reset enabled

When oscillation stop is detected;

CLKSTP2 is set to “1”.

Internal RESET occurs.

Oscillation stop detection reset enabled

When oscillation stop is detected;

CLKSTP2 is set to “1”.

Internal RESET occurs.

Reset

released

CLKM54 = 102

CLKM54 = 002

(Note 1)

CLKM54=102

CLKM54=002

(Note 1)

State 3 XIN oscillation

: enabled

Low-speed on-chip oscillator : enabled

State 3'

XIN oscillation

: enabled

Low-speed on-chip oscillator : enabled

XIN

: enabled

High-speed on-chip oscillator : stop

Low-speed on-chip oscillator : enabled

CLKSTP1

CLKSTP1 = 12

State 2'

CLKSTP1= 12

XIN

: enabled

High-speed on-chip oscillator: stop

Low-speed on-chip oscillator : enabled

Reset

released

XIN oscillation

: enabled

Low-speed on-chip oscillator : enabled

XIN oscillation

: enabled

Low-speed on-chip oscillator : enabled

State 2

(Note 2)

φSOURCE: XIN

φSOURCE: Low-speed on-chip oscillator (Note 4)

Oscillation stop detection

circuit is in active. (Note 3)

State 2'a (Note 2)

Oscillation stop detection reset disabled

When oscillation stop is detected;

CLKSTP2 is set to "1".

Internal RESET does not occur.

7549 Datasheet(PDF) 49 Page - Renesas Technology Corp

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