M16C26 Datasheet, PDF (42/239 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 bit (CM20)
You can start the oscillation stop detection by setting this bit to “1”. The detection is not executed when
this bit is set to “0” or in reset status. Be sure to set this bit to “0” before setting for the stop-mode. Set this
bit again to “1” after release from stop-mode. This is because it is necessary to cancel the oscillation stop
detection function due to a certain period of unstable oscillation after release from stop-mode. Set this bit
to “0” also before setting the main clock stop bit (bit 5 at 000616) to “1”.
Do not set this bit to “1” if the frequency of XIN is lower than 2 MHz.
Main clock switch bit (CM21)
You can use the ring oscillator as a system clock by setting this bit to “1”. When this bit is "0", the ring
oscillator is not in operation. For more explanation, see the section of the clock generating circuit.
Oscillation stop detection status (CM22)
You can see the status of the oscillation stop detection. When this bit is “1”, an oscillation stop is de-
tected. For usage of this bit, see the explanation on CM27.
Clock monitor bit (CM23)
You can see the operation status of the XIN clock. When this bit is “0”, XIN is operating correctly. You can
check the operation status of XIN when an oscillation stop detection interrupt is generated.
Operation select (when an oscillation stop is detected) bit (CM27)
(1) Operation when internal reset is selected (CM27 is set to “0”.)
An internal reset is generated when an abnormal stop of XIN is detected. The microcomputer stops in
reset status and does not operate further.
Note: Release from this status is only possible through an external reset. However, in case of a
defect XIN clock, further operation cannot be compensated.
All ports are configured to input port (floating) after an internal reset is generated.
(2) Operation when oscillation stop detection interrupt is selected (CM27 is set to “1”.)
An oscillation stop detection interrupt is generated when an abnormal stop of XIN is detected. The ring
oscillator starts operation instead of the XIN clock which stopped abnormally. The operation goes further
with the supply from the ring oscillator. For the oscillation stop detection interrupt judgement on the
interrupt condition is necessary, because this interrupt shares the vector table with watchdog timer inter-
rupt. Use the oscillation stop detection status (CM22) for the judgment. By clearing CM22, the accep-
tance of oscillation stop detection interrupt resumes. Figure 1.8.7 shows the flow of the judgment.
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