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NOTICE TO USER
The information contained in this manual is believed to be correct. However, MicroBee Systems
assumes no responsibility for any of the circuits described herein, conveys no license under any
patent or other right, and makes no representations that the circuits are free from patent
infringement. MicroBee Systems makes no representation or warranty that such applications will
be suitable for the use specified without further testing or modification.
MicroBee Systems Corporation general policy does not recommend the use of its products in life
support applications where the failure or malfunction of a component may directly threaten life or
injury. It is a Condition of Sale that the user of MicroBee Systems products in life support
applications assumes the risk of such use and indemnifies MicroBee Systems against all
damage.
Please read before installing your product.
MicroBee’s products are designed to be high in performance while consuming very little power. In
order to maintain this advantage, CMOS circuitry is used. CMOS chips have specific needs and
some special requirements that the user must be aware of. Read the following to help avoid
damage to your card from the use of CMOS chips.
Using CMOS Circuitry
Industrial Control originally used LSTTL circuits. Because many PC components are used in
laptop computers, IC manufacturers are exclusively using CMOS technology. Both TTL and
CMOS have failure mechanisms, but they are different. This section describes some of the
common failures which are common to all manufacturers of CMOS equipment.
Improper power causes catastrophic failure.
If a card has had reverse polarity or high voltage applied, replacing a failed component is not an
adequate fix. Other components probably have been partially damaged or a failure mechanism
has been induced. Therefore, a failure will probably occur in the future. For such cards, MicroBee
highly recommends that these cards be replaced.
Other over-voltage symptoms
In over-voltage situations, the programmable logic devices, EPROM’s and CPU chips, usually fail
in this order. The failed device may be hot to the touch. It is usually the case that only one IC will
be overheated at a time.
Power sequencing
The possibility of failure can be caused by the external application of input voltage to the radio via
the external B+ input while the PCFW-104 power is off. If you apply 5V to the input of a TTL chip
with the power off, nothing will happen. Applying a 5V input to a CMOS card will cause the
current to flow through the input and out the 5V power pin. This current attempts to power up the
card. Most inputs are rated at 25 mA maximum. When this is exceeded, the chip may be
damaged.
Failure on power-up
Even when there is not enough current to destroy an input described above, the chip may be
destroyed when the power to the card is applied. This is due to the fact that the input current
biases the IC so that it acts as a forward biased diode on power-up. This type of failure is typical
on serial interface chips.
Hot insertion
Plugging cards into the card cage with the power on will usually not cause a problem. (MicroBee
urges that you do not do this!)
However, the card may be damaged if the right sequence of pins contacts as the card is pushed
into the socket. This usually damages bus driver chips and they may become hot when the power
is applied. This is one of the most common failures of expansion cards.
