55
38C2 Group
SINGLE-CHIP 8-BIT CMOS MICROCOMPUTER
MITSUBISHI MICROCOMPUTERS
PRELIMINAR
Y
Notice:
This
is not
a final
specification.
Some
parametric
limits
are
subject
to change.
(3) Oscillator concerns
Take care to prevent an oscillator that generates clocks for a micro-
computer operation from being affected by other signals.
Keeping oscillator away from large current signal lines
Install a microcomputer (and especially an oscillator) as far as pos-
sible from signal lines where a current larger than the tolerance of
current value flows.
q Reason
In the system using a microcomputer, there are signal lines for
controlling motors, LEDs, and thermal heads or others. When a
large current flows through those signal lines, strong noise occurs
because of mutual inductance.
Fig. 59 Wiring for a large current signal line/Wiring of signal lines where potential levels change frequently
Installing oscillator away from signal lines where potential levels
change frequently
Install an oscillator and a connecting pattern of an oscillator away
from signal lines where potential levels change frequently. Also,
do not cross such signal lines over the clock lines or the signal
lines which are sensitive to noise.
q Reason
Signal lines where potential levels change frequently (such as the
CNTR pin signal line) may affect other lines at signal rising edge
or falling edge. If such lines cross over a clock line, clock wave-
forms may be deformed, which causes a microcomputer failure or
a program runaway.
XIN
XOUT
VSS
M
Microcomputer
Mutual inductance
Large
current
GND
XIN
XOUT
VSS
CNTR
Do not cross
N.G.
Keeping oscillator away from large current signal lines
Installing oscillator away from signal lines where potential levels
change frequently
CNVSS/VPP
VSS
About 10k
(4) Wiring to VPP pin of flash memory version
Connect an approximately 10 k
resistor to the VPP pin the shortest
possible in series and also to the VSS pin.
Note: Even when a circuit which included an approximately 10 k
resistor is used in the Mask ROM version, the microcomputer
operates correctly.
q Reason
The VPP pin of the flash memory version is the power source input
pin for the built-in flash memory. When programming/erasing in the
built-in flash memory, the impedance of the VPP pin is low to allow the
electric current for writing/erasing flow into the flash memory. Be-
cause of this, noise can enter easily. If noise enters the VPP pin, ab-
normal instruction codes or data are read from the built-in flash
memory, which may cause a program runaway.
Fig. 60 Wiring for the VPP pin of flash memory