Subject:                        Time:    1:58
PM
                            hardware or software
2/18/99
                                                             Date:
In a recent thread, (hardware or software), there seem to be a final
conclusion that an I/O pin was floating and that the solution was to program
all unused I/O pins as inputs and wire them to ground (Vss).  I always used
to think that programming unused I/O pins as outputs would be enough.
Isn't it possible that this is still true for all pins except Port A bit 4
(RA4)?

In all the other cases the I/O pin when an output is connected to a data
latch and is pulled to eithe Vdd or Vss.  Since the TTL input buffer is
also connected to the I/O pin, it will be pulled either high or low.

The only exception is RA4 which is an open drain.  The data latch can't
pull it to Vdd, only to Vss.  So, isn't the conclusion then: put a resistor
on RA4 to Vdd and program it to output or program RA4 to input and wire
the pin to Vss or Vdd?  All other unused I/O pins can be just set to
output,(or set to input and wired high or low as proposed).  No?

BTW, does TTL input mean that actual bipolar transistors are used on the
chip?

Stan