Fujitsu MB90390 Series, Hardware Manual, Page: 52 / 740

24
CHAPTER 1 OVERVIEW
●
Crystal Oscillator Circuit
Noises around X0 or X1 pins may be possible causes of abnormal operations. Make sure to provide bypass
capacitors via shortest distance from X0, X1 pins, crystal oscillator (or ceramic resonator) and ground lines,
and make sure, to the utmost effort, that lines of oscillation circuit not cross the lines of other circuits.
It is highly recommended to provide a printed circuit board art work surrounding X0 and X1 pins with a
ground area for stabilizing the operation. Please ask the crystal maker to evaluate the oscillational
characteristics of the crystal and this device.
●
Turning-on Sequence of Power Supply to A/D Converter and Analog Inputs
Make sure to turn on the A/D converter power supply (AV
CC
, AVRH, AVRL) and analog inputs (AN0 to
AN14) after turning-on the digital power supply (V
CC
). Turn-off the digital power after turning off the A/D
converter supply and analog inputs. In this case, make sure that the voltage not exceed AVRH or AV
CC
.
●
Connection of Unused Pins of A/D Converter if A/D Converter is unused
Connect unused pins of A/D converter to AV
CC
= V
CC
, AV
SS
= AVRH = AVRL = V
SS
.
●
Precautions at power on
To prevent a malfunction of the internal step-down circuit, the voltage rise time at power-on should be 50
μ
s or more (between 0.2 V and 2.7 V).
●
Note on operation during PLL clock mode
On this microcontroller, if in case the crystal oscillator breaks off or an external reference clock input stops
while the PLL clock mode is selected, a self-oscillator circuit contained in the PLL may continue its
operation at its self-running frequency. However, Fujitsu will not guarantee results of operations if such
failure occurs.