Elan Digital Systems Ltd.
55
HD717 USER’S
GUIDE
7. OPERATIONAL PRECAUTIONS
Unless otherwise stated, all voltage levels are referenced to the HD717’s GND PIN.
All points apply equally to HD717,712,713.
•
Don’t leave active signals connected to the digital IOPINS that are
capable of sourcing more than a few mA whilst the HD717 itself is
unpowered. This could lead to “reverse powering” the card via its
inputs which can cause latch-up and destruction of internal cmos
devices. If there is a possibility of this condition occurring, you are
advised to connect series resistors between your drivers and the
HD717’s inputs to affect current limiting (typ 4k7). Remember that
this will slow the edges of the digital signals.
•
Don’t draw excessive current from Vcc. The limit is shown in the
pinout table. Doing so will adversely effect the HD717’s
performance and could cause damage.
•
The 32 way IO connector is quite delicate. Don’t stress it unduly.
•
Don’t apply digital inputs to the HD717 that are greater than (system
Vcc + 0.5v) where “system Vcc” is the level provided on the
HD717’s Vcc output pin. Doing so will damage the HD717.
Likewise, don’t apply levels that are less than -0.5v to the digital
inputs.
•
Don’t short circuit any of the HD717’s outputs to ground or to other
outputs. This will damage the HD717.
•
Ensure that the card’s main 5v power input on the pcmcia 68 way
connector does not exceed 7.0v as this will damage internal devices.
This is normally not a factor that the user of a “standard” pcmcia slot
needs to consider. However, under fault conditions or an embedded
design this condition may need to be given some thought to avoid
damaging the HD717.
