Mitsubishi microcomputers
M16C / 6N0 / 6N1 Group
SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER
48
Power Control
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
register. When this bit is set to "1", the function is enabled. After the reset is released, the oscillation stop
detection function becomes invalid because the bit value is "0".
Note that an oscillator input signal that violates the timing or voltage specification for XIN may cause the
CPU to hang. Therefore the oscillation stop detection interrupt may not be processed. Countermeasures
on system level should be taken for the CPU to recover from such kind of status.
Table 1.10.5 gives an specification overview of the oscillation stop detection function.
Table 1.10.5. Specification outlint of the oscillation stop detection function
Figure 1.10.8. Structure of the oscillation stop detection circuit
CM21
Internal reset
generating cicuit
Oscillation stop
detection interrupt
generating circuit
Charge/discharge
cicuit
Ring oscillator
Internal reset
To the CPU
Watchdog timer
interrupt
Main clock
Main clock switch control
To the main clock
prescaler
Compulsory discharge when CM20="0"
Pulse generation
circuit for clock edge
discharge control
detection and charge/
Note
XIN
Note: 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.
Item
Oscillation stop detectable clock and
frequency range
Enabling condition for oscillation stop
detection function
Operation at oscillation stop detection
Notes on STOP mode
Specification
XIN : 2MHz or higher
When the oscillation stop detection bit (bit 0 of address 000C16)
is set to "1"
When internal reset is generated (bit 7 at address 000C16 is
cleared to "0".)
When oscillation stop detection interrupt is generated (bit 7 at
address 000C16 is set to "1".)
Before setting up the stop mode, write "0" in the oscillation stop
detection valid bit to invalidate the oscillation stop detection func-
tion. Write "1" into the bit again after the stop mode is released.