M16CSLASH26 datasheet(40/239 Pages) RENESAS

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Renesas Technology Corp.

Oscillation Stop Detection

M16C/26 Group

SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER

Under

development

Preliminary Specifications Rev. 0.9

Specifications in this manual are tentative and subject to change.

Oscillation Stop Detection Function

The oscillation stop detection function detects abnormal stopping of the clock by causes such as opening

and shorting of the XIN oscillation circuit. When oscillation stop is detected, either an internal reset or an

oscillation stop detection interrupt is generated. The selection depends on the value in the bit 7 of the

oscillation stop detection register (address 000C16). When an oscillation stop detection interrupt is gener-

ated, the ring oscillator in the microcomputer operates automatically and is used as the system clock in

place of the XIN clock. This allows interrupt processing.

The oscillation stop detection function can be enabled/disabled with bit 0 of the oscillation stop detection

detection function becomes disabled because the bit value is “0.”

Table 1.8.2 gives an specification overview of the oscillation stop detection function, Figure 1.8.5 is a

configuration diagram of the oscillation stop detection circuit and Figure 1.8.6 shows the configuration of

the oscillation stop detection register.

Table 1.8.2. Specification overview of the oscillation stop detection function

Item

Specification

Oscillation stop detectable clock

f(XIN)

³ 2 MHz

and frequency bandwidth

Enabling condition for oscillation

When the oscillation stop detection bit (bit 0 of address 000C16)

stop detection function

is set to “1”

Operation at oscillation stop,

• Internal reset occurs (when bit CM27 = "0")

re-oscillation detection

• Oscillation stop, re-oscillation detection interrupt occurs (when bit

CM27 = “1”)

Notes on STOP mode

Before setting up the stop mode, write “0” in the oscillation stop

detection enable bit to disable the oscillation stop detection function.

Write "1" in the bit again after the stop mode is.

XIN

CM21, CM20

CM07

#:When XIN is supplied, this repeats charge and discharge with pulses by XIN edge detection.

When XIN is not supplied, this continues charging. When the charge exceeds a certain level,

it regards the oscillation as stopped.

Pulse generation

circuit for clock

edge detection

and charge/

discharge control

Charge/

discharge

circuit

Oscillation stop

detection interrupt

generating circuit

Ring oscillator

Watchdog

timer

interrupt

To the CPU

Main clock

To the main clock

division circuit

Main clock switch control

Internal reset

generating circuit

Figure 1.8.5. Oscillation stop detection circuit

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