How can I handle unused pins of ports of a microcomputer?
Answer : If you leave unused input pins open, malfunctions and latch up may occur. To avoid such problems, we recommend to pull up
or down the unused input pins by using a resistor of 2kW.
Can I pull up or down the unused pins by grouping them using a single resistor?
Answer : We do not recommend to pull up or down the unused pins by grouping them by using a single resistor because events such as
collisions in pin output level may occur during runaway.
Can I connect an inductor directly to the power supply?
Answer : We do not recommend to connect an inductor directly to the power supply. Before inserting the inductor, connect a capacitor
between the inductor and the power supply of a microcomputer.
If the following events occur in the C pin, how does the microcomputer operate? (1) open, (2) connected to VDD, (3) connected
to GND.
Answer : (1) Internal voltage becomes unstable, possibly resulting (2) Withstand voltage of the internal circuit is exceeded and
the life of a microcomputer is shortened remarkably, possibly resulting in chip failure. (3) The internal voltage of the
microcomputer eventually becomes 0 V and the microcomputer does not run. Moreover, the current path from the power supply
is formed, possibly resulting in chip failure.
For a microcomputer with a pair of Vcc pins and a pair of Vss pins, what will happen if one of each pair becomes open?
Answer : We consider that there will be no problem from a viewpoint of device capabilities. However, unnecessary radiation may increase,
malfunctions may occur due to increase in ground level, and the total output current standards may not be satisfied. The
following are described in the data sheet: - If there are two or more Vcc and Vss pins, from a device design viewpoint, the
pins that need be at the same potential are connected within the device to prevent malfunctions such as latch-up. Be sure,
however, to connect all of these pins externally to the power supply or ground to reduce unnecessary radiation, prevent strobe
signal malfunctions caused from increase in ground level, and follow the total output current standards.
The capacitor capacitance for the C pin is described as 1.0 uF (MAX) in the data sheet. What happens when I use a capacitor
having a capacitance of greater than1.0mF?
Answer : The internal voltage step down circuit forms a loop back and so oscillation may occur due to a large capacitance of the C
pin. If oscillation occurs internally, that makes a microcomputer to run away.
When a level of a mode pin has changed during microcomputer operation, how much time it takes to transfer to each mode?
Answer : The voltage level of the mode pin is input as an internal control signal. So, a transfer to each mode occurs immediately after
the pin level changes. (The latch type of the mode pin is supported from MB903XX series and later.)
How much capacitance of a capacity can be added to a port?
Answer : 1) For I/O ports, you should consider current that flows when external capacity is charged or discharged. In general, we recommend
about 100, or 200 pF.If you need larger capacity, consult us separately. 2) No special restrictions is applied to input-specific
ports.
If the following events occur when unusing the sub-clock, what operations occur? (Conditions of unused sub-clock:X0A → pull
down, X1A → open) (1) X0A pin: open, (2) X1A pin: connected to VDD pin, (3) X1A pin: connected to GND pin. (Target: MB90495
series)
Answer : (1) Both X0A and X1A pins will become open and the penetration current of the oscillator circuit may flow. We consider that
there are no particular problems with other operations. (2) We consider that there are no particular problems. (3) The leakage
current will increase in the oscillation circuit, possibly resulting in device failures.
If the following events occur under the internal vector mode use conditions, how does the CPU operator? (Internal vector mode:
MOD2=0, MOD1=1, MOD0=1) (1) MOD0 pin: open, (2) MOD0 pin: connected to GND, (3) MOD1 pin: open, (4) MOD1 pin: connected to
GND, (5) MOD2 pin: open, (6) MOD2 pin: connected to VDD.
Answer : (1), (3), and (5) Because these pins are used to set modes, the CPU may run away. (2) The CPU may run away. (When MD2=0,
MD1=1, and MD0=0 occur, the mode transits to external vector mode 2 and the CPU finally attempts to make an external access.
This may cause the CPU to run away.) (4) The CPU may run away. (If MD2=0, MD1=0, and MD0=1 occur, the mode transfers to external
vector mode 1 and the CPU finally attempts to make an external access. This may cause the CPU to run away.) (6) The CPU may
run away. (When MD2=1,MD1=1, and MD0=1 occur, the mode transfers to the Flash memory mode and the CPU finally attempts to
make an external access. This may cause the CPU to run away.)
If the following events occur in the power supply pin of the AD converter, how does the A/D converter operate? (1) AVcc pin:
open, (2) AVRH pin: open, (3) AVRL pin: open, (4) AVss pin: open.
Answer : (1), (4) A/D converter operations cannot be assured. We consider, however, that no particular problems occur with other operations
from a viewpoint of device capabilities. (2), (3) The converted values of the A/D converter are unpredictable. We consider,
however, that no problems occur in other converters.
Answer : When oscillation completely stops, the pin holds the status it had before oscillation stops. The microcomputer, however, may
run away due to abnormal oscillation occurring until oscillation stops.
The data sheet recommends free pin treatment. Which of the following settings requires less MCU current consumption? - "H"
or "L" output setting in OEPN - L input in input setting
Answer : There is no difference between MCU current consumption in these settings.
Is it all right if only VIH is recognized as aN "H" level in an input port in use? Also is it necessary to consider input
current?
Answer : Consider only VIH on the data sheet. To stretch a point, it is thinkable that depending on the value of the resistor connected
to the input port, difference in internal capacity charge time tends to influence the level switching timing.
When a microcomputer power is off (not fixed to 0 V), can the +B input be supported?
Answer : The maximum clamping current and total maximum clamping current are specified by absolute maximum ratings. +B input can be
made by limiting current even when the microcomputer power is off.
The manual mentions that leaving an unused input pin open may cause permanent breakage by a malfunction or latch-up, so you
should perform pull-up or pull-down treatment with a resistor of 2kW or higher. Does this mean that I should connect the unused
input pin to VSS and perform pull-down treatment via a resistor of 2kW or higher? I cannot understand the reason why it is
not good to connect the unused pin directly to VSS. What is the cause?
Answer : The purpose of this item is to fix input pin level, so fix the level of the target pin via a resistor. Please assume that
resistors are used to restrict current when the targe pin serves as an output pin due to a microcomputer runaway, etc.
I think that a port internally has diodes. Can I use them for clamping?
Answer : When you use diodes in the port intentionally, use the diode within the clamping current capacity specified in a data sheet
to prevent a problem. To use the diode without this capacity, provide external clamping.
The data sheet clearly describes that the RESET pin contains a pull-up resistor. However, for use with the reset IC, does
the pin need be externally pulled up?
Answer : The pin need not be externally pulled up.
What is the meaning of the description that "Prevention of malfunctions of the strobe signals due to increase in the ground
level" in the item "Power Supply Pins" in "Device Handling" in the data sheet?
Answer : The devices inside a microcomputer are operating, obtaining timings from strobe signals used as a certain reference. (A rising
or falling edge timing is generally used.) The description clearly means that, when the GND level increases, the system cannot
recognize a falling or rising edge, possibly resulting in abnormal address latching and resource operations.
CMOS hysteresis input standards are described in the data sheet but I cannot identify the hysteresis width although I increased
or decreased Vcc within 0 V to 5 V on the constant voltage power supply. (The level always switches to "H" or "L"
near 1/2Vcc.) (Target: MB90548 series)
Answer : You cannot identify the hysteresis width in the method for increasing or decreasing voltage in seconds like the constant voltage
power supply. Voltage increase and decrease in milliseconds are required.
For +B input to a pin, how much voltage is applied to the pin?
Answer : When current is made to be equal to or less than the standard value by using the limit resistor, the voltage of 5 V is applied
to the pin. However, since the protection diode is built into the microcomputer, the voltage that is about 0.5 higher is actually
applied to the pin.
When +B input is made, what voltage is applied to the pin?
Answer : Since the protection diode is used, the pin voltage becomes the voltage of Vcc + diode (approx. 0.6 V). (For Vcc = 5 V, the
pin voltage is 5.6 V. For +B input, the current limit resistor is required.)
When reset input is canceled with clocks removed, MB90545G series etc. enter a pin status that occurred before clock removal.
However, are there microcomputers whose specifications describe that Hi-z is set even after reset cancellation? (Target: MB90340/350
series)
Answer : The pins of MB90340 and MB90350 hold Hi-z even when reset input is cancelled with clocks removed.
Why do MB90590G series and MB90595G series differ in VILS and VILR? (Target: MB90590G,MB90595G)
Answer : There is no same change because an internal circuit differs for MB90595G series. The current MB90595G standard is "VILS
→ 0.2 Vcc" and no VILR standard is available. (Checked by FMC.)
