7546 datasheet(63/95 Pages) RENESAS

63 / 95 page

Rev.1.21

Nov 15, 2006

page 63 of 93

REJ03B0160-0121

7546 Group

Fig. 79 Structure of MISRG

q Oscillation stop detection circuit

The oscillation stop detection circuit is used for reset occurrence

when a ceramic resonator or RC oscillation circuit stops by dis-

connection. 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

ceramic or RC oscillation stop detection function active bit. When

the oscillation stop detection circuit is in active, ceramic or RC os-

cillation is watched by the on-chip oscillator. When stop of ceramic

or RC oscillation is detected, the oscillation stop detection status

bit is set to “1”. While “1” is set to the oscillation stop reset bit, in-

ternal reset occurs when oscillation stop is detected.

The external reset and the oscillation stop reset can be discrimi-

nated by reading the oscillation stop detection status bit.

The oscillation stop detection status bit retains “1”, not initialized,

when the oscillation stop reset occurs. The oscillation stop detec-

tion status bit is initialized to “0” when the external reset occurs.

Accordingly, reset by oscillation stop can be confirmed by using

this flag.

s Notes on Oscillation Stop Detection Circuit

• Do not execute the transition to “state 2’a” shown in Figure 80

because in this “state 2’a”, MCU is stopped without reset even

when XIN oscillation is stopped.

• Ceramic or RC oscillation stop detection function active bit is not

cleared by the oscillation stop internal reset. Accordingly, the

oscillation stop detection circuit is in active when system is re-

leased from internal reset cause of oscillation stop detection.

• Oscillation stop detection status bit is initialized by the following

operation.

(1) External reset

(2) Write “0” data to the ceramic or RC oscillation stop detection

function active bit.

• The oscillation stop detection circuit is not included in the emu-

lator MCU “M37542RSS”.

MISRG(address 003816, initial value: 0016)

Oscillation stabilization time set bit after

release of the STP instruction

0: Set “0116” in timer1, and “FF16”

in prescaler 1 automatically

1: Not set automatically

Reserved bits

(Do not write “1” to these bits)

Not used (return “0” when read)

Oscillation stop detection status bit

0: Oscillation stop not detected

1: Oscillation stop detected

Oscillation stop reset bit

0: Oscillation stop reset disabled

1: Oscillation stop reset enabled

Ceramic or RC oscillation stop

detection function active bit

0: Detection function inactive

1: Detection function active

7546 Datasheet(PDF) 63 Page - Renesas Technology Corp

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