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Failure on powerup: 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 powerup. This type of failure is typical on serial interface
chips but can apply any IC on the card.
•
Under rated power supply: The board may fail to boot due to
an under rated power supply. It is important that a quality power
supply be used with Octagon Systems cards that has sufficient
current capacity, line and load regulation, hold up time, current
limiting, and minimum ripple. It is extremely import to select a
supply that ramps up in 10ms or less. This assures that all the
circuitry on the CPU Cards sequences properly and avoids system
lockup.
•
Excessive signal lead lengths: Another source of failure that
was identified years ago at Octagon was excessive lead lengths on
digital inputs. Long leads act as an antenna to pick up noise.
They can also act as unterminated transmission lines. When 5V is
switch onto a line, it creates a transient waveform. Octagon has
seen sub-microsecond pulses of 8V or more. The solution is to
place a capacitor, for example 0.1 µF, across the switch contact.
This will also eliminate radio frequency and other high frequency
pickup.
5
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