NOTICE TO USER
...............................................................................................................
The information contained in this manual is believed to be correct. However, MicroBee Sys-
tems 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 appli-
cations 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 threat-
en 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 mecha-
nism 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
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Summary of Contents for PCFW-104-ETH
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