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3850 Group (Spec. H) User’s Manual
3-37
APPENDIX
3.3 Notes on use
3.3.7 Notes on A-D converter
(1)
Analog input pin
Make the signal source impedance for analog input low, or equip an analog input pin with an external
capacitor of 0.01
F to 1 F. Further, be sure to verify the operation of application products on the
user side.
q Reason
An analog input pin includes the capacitor for analog voltage comparison. Accordingly, when
signals from signal source with high impedance are input to an analog input pin, charge and
discharge noise generates. This may cause the A-D conversion precision to be worse.
(2)
A-D converter power source pin
The AVSS pin is A-D converter power source pin. Regardless of using the A-D conversion function
or not, connect it as following :
AVSS : Connect to the VSS line
q Reason
If the AVSS pin is opened, the microcomputer may have a failure because of noise or others.
(3)
Clock frequency during A-D conversion
The comparator consists of a capacity coupling, and a charge of the capacity will be lost if the clock
frequency is too low. Thus, make sure the following during an A-D conversion.
f(XIN) is 500 kHz or more in middle-/high-speed mode.
Do not execute the STP instruction.
When the A-D converter is operated at low-speed mode, f(XIN) do not have the lower limit of
frequency, because of the A-D converter has a built-in self-oscillation circuit.
3.3.8 Notes on watchdog timer
qMake sure that the watchdog timer does not underflow while waiting Stop release, because the watchdog
timer keeps counting during that term.
qWhen the STP instruction disable bit has been set to “1”, it is impossible to switch it to “0” by a program.
3.3.6 Notes on PWM
The PWM starts after the PWM enable bit is set to enable and “L” level is output from the PWM pin.
The length of this “L“ level output is as follows:
sec.
(Count source selection bit = “0”, where n is the value set in the prescaler)
sec.
(Count source selection bit = “1”, where n is the value set in the prescaler)
n + 1
2 f(XIN)
n + 1
f(XIN)