Although there is also a signal on the
ACK line of the Centronics interface in
emulator mode (unless JP6 is
swapped), this of little consequence because
the BUSY line is held high permanently
in run mode. If you use P4.0
as an input, make sure that the line
does not short-circuit the output of
your application when emulator mode
is used. It is, therefore, recommended
to drive P4.0 from an open-collector or
open-drain output. This avoids the risk
of short-circuits, while a pull-up resistor
is not required because it is already
contained in the controller.
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