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M16C/5L Group, M16C/56 Group
8.7.2
Operation When CM27 Bit is 1 (Oscillator Stop/Restart Detect Interrupt)
When the CM20 bit is 1 (oscillator stop/restart detect function enabled), the system is placed in the
state shown in Table 8.7 if the main clock detects oscillator stop or restart.
The CM21 bit becomes 1 in high-speed, medium-speed, or low-speed mode. The FRA01 bit does not
change. Thus, high-speed and medium-speed mode become 125 kHz on-chip oscillator mode or 40
MHz on-chip oscillator mode. Because the CM07 bit does not change, low-speed mode remains in low-
speed mode, but fOCO-S or fOCO-F becomes the clock source for the peripheral functions.
When the CM21 bit is set to 1, the CM14 bit becomes 0 (125 kHz on-chip oscillator on), but the FRA00
bit does not change (40 MHz on-chip oscillator does not oscillate automatically). Thus, when the
FRA01 bit is 1 (40 MHz on-chip oscillator selected), set the FRA00 bit to 1 (40 MHz on-chip oscillator
on). Do not set the FRA00 bit to 0 while the FRA01 bit is 1, and vice versa.
Since the CM21 bit does not change in PLL operating mode, change the mode to 125 kHz on-chip
oscillator mode or 40 MHz on-chip oscillator mode in the interrupt routine.
Table 8.7
State after Oscillator Stop/Restart Detect When CM27 Bit is 1
Condition
High-speed mode
Medium-speed
mode
Main clock
Low-speed mode
oscillator stop
40 MHz on-chip
detected
oscillator mode
125 kHz on-chip
oscillator mode
PLL operating mode
Main clock
oscillator
-
restart
detected
CM14 bit: Bit in the CM1 register
Bits CM21, CM22, CM23: Bits in the CM2 register
Notes:
1.
fOCO-S or fOCO-F is selected depending on the FRA01 bit setting.
2.
fC is used as the CPU clock in low-speed mode.
R01UH0127EJ0110 Rev.1.10
Sep 01, 2011
•
Oscillator stop/restart detect interrupt is generated
•
CM14 bit is 0 (125 kHz on-chip oscillator on)
•
CM21 bit is 1 (fOCO-S or fOCO-F is used as the clock source for
the CPU and peripheral function clocks)
•
CM22 bit is 1 (main clock stop detected)
•
CM23 bit is 1 (main clock stopped)
•
Oscillator stop/restart detect interrupt is generated
•
CM14 bit is 0 (125 kHz on-chip oscillator on)
•
CM21 bit remains unchanged
•
CM22 bit is 1 (main clock stop detected)
•
CM23 bit is 1 (main clock stopped)
•
Oscillator stop/restart detect interrupt is generated
•
CM14 bit is 0 (125 kHz on-chip oscillator on)
•
CM21 bit does not change
•
CM22 bit is 1 (main clock stop detected)
•
CM23 bit is 0 (main clock oscillating)
After Detection
(1, 2)
8. Clock Generator
Page 112 of 803
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