M16C Datasheet, PDF (48/262 Pages) Mitsubishi Electric Semiconductor – SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER

Preliminary Specifications REV.B
Mitsubishi microcomputers
Specifications in this manual are tentative and subject to change.
M16C / 6N Group
SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER
Oscillation Stop Detection Function
Oscillation Stop Detection Function
This function is for detecting an abnormal stop of the clock which is caused by open- and/or short circuit of
the Xin oscillation circuit. When it detects an oscillation stop, it generates either an internal reset or an
oscillation stop detection interrupt. The selection depends on the value in the bit 7 of the oscillation stop
detection register (000C₁₆). When an oscillation stop detection interrupt is generated, the ring oscillator which
is built in the microcomputer starts oscillation automatically, which is used as the system clock instead of
Xin. Through this an interrupt operation is enabled.
You can set the function to valid/invalid by changing the value in the bit 0 of the oscillation stop detection
register. The function is valid when the bit is "1". However, the value of the bit after reset release is "0", so the
function is invalid.
Table 5-5. Outline of specification of the oscillation stop detection function
Item
Specification
Clock and Frequency
Xin is 2 Mhz or more.
Condition
Operation when detected
an oscillation stop
In the stop-mode
The oscillation stop detection bit (bit 0 at 000C16) is "1".
#Generates an internal reset (when the bit 7 at 000C16 is "0")
#Generates an oscillation stop detection interrupt (when the bit 7 at
000C16 is "1")
Write "0" in the oscillation stop detection bit before setup of the stop-
mode to set the oscillation stop detection function to "invalid". Write
"1" in the bit after stop-mode release.
Compulsory discharge when CM20=0
Charge/discharge
cicuit
Pulse generation
Xin
circuit for clock edge
detection and charge/
discharge control
Internal reset
generating cicuit
Oscillation stop
detection interrupt
generating circuit
Watchdog timer
interrupt
Internal reset
To the CPU
#
CM21
Main clock switch control
Ring oscillator
Main clock
To the main clock
prescaler
#: 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 5-8. Structure of the oscillation stop detection circuit
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