M16C26 Datasheet, PDF (40/239 Pages) Renesas Technology Corp – 16-BIT CMOS SINGLE-CHIP MICROCOMPUTER M16C FAMILY / M16C/20 SERIES

Udenvdeelropment
Preliminary Specifications Rev. 0.9
Specifications in this manual are tentative
Oscillation Stop Detection
and
subject to change.
SINGLE-CHIP 16-BIT
M16C/26 Group
CMOS MICROCOMPUTER
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 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.
Pulse generation
XIN
circuit for clock
edge detection
Charge/
discharge
and charge/
circuit
0
Internal reset
generating circuit
1
Oscillation stop
detection interrupt
discharge control
generating circuit
CM07
Watchdog
timer
interrupt
CM21, CM20
Internal reset
To the CPU
Ring oscillator
Main clock switch control
11
01
Main clock ^{To the main clock}
division circuit
#: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.
Figure 1.8.5. Oscillation stop detection circuit
34
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