
3802 GROUP USER’S MANUAL
3-24
APPENDIX
3.3 Notes on use
(2) AV
SS
pin
Connect a power source for the A-D converter, AV
SS
pin to the V
SS
line of the analog circuit.
(3) A clock frequency during an 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.
G
f(X
IN
) is 500 kHz or more .
(When the ONW pin is "L", f(X
IN
) is 1 MHz or more.)
G
Do not execute the STP instruction and WIT instruction.
3.3.4 Notes on the RESET pin
When a rising time of the reset signal is long, connect a ceramic capacitor or others across the RESET pin and
the V
SS
pin. And use a 1000 pF or more capacitor for high frequency use. When connecting the capacitor, make
sure the following :
G
Make the length of the wiring which is connected to a capacitor the shortest possible.
G
Make sure to check the operation of application products on the user side.
Reason
If the several nanosecond or several ten nanosecond impulse noise enters the RESET pin, a microcomputer may
malfunction.
3.3.5 Notes on input and output pins
(1) Fix of a port input level in stand-by state
Fix input levels of an input and an I/O port for getting effect of low-power dissipation in stand-by state, especially
for the I/O ports of the N-channel open-drain.
Pull-up (connect the port to V
CC
) or pull-down (connect the port to V
SS
) these ports through a resistor.
When determining a resistance value, make sure the following:
G
External circuit
G
Variation of output levels during the ordinary operation
*
stand-by state : the stop mode by executing the
STP
instruction
WIT
instruction
Reason
Even when setting as an output port with its direction register, in the following state :
G
N-channel......when the content of the port latch is “1”
the transistor becomes the OFF state, which causes the ports to be the high-impedance state. Make sure that the
level becomes “undefined” depending on external circuits.
Accordingly, the potential which is input to the input buffer in a microcomputer is unstable in the state that input
levels of an input and an I/O port are “undefined.” This may cause power source current.
(2) Modify of the content of I/O port latch
When the content of the port latch of an I/O port is modified with the bit managing instruction*, the value of the
unspecified bit may be changed.
Reason
The bit managing instruction is read-modify-write instruction for reading and writing data by a byte unit.
Accordingly, when this instruction is executed on one bit of the port latch of an I/O port, the following is executed
to all bits of the port latch.
G
As for a bit which is set as an input port : The pin state is read in the CPU, and is written to this bit after bit
managing.
G
As for a bit which is set as an output port : The bit value is read in the CPU, and is written to this bit after bit
managing.