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'unused data lines on pic16c5x '
1994\07\27@120650 by mycal



I've done a project where I use only one data line on a pic16c54, it
is RA0 and it is set to output.  All other pins are set to input (default),
as I set port_a by :
       movlw 0eh
       tris  port_A

and don't init port_b.  Ok everything is fine here.  I am generating
a repeating pattern out of RA0, but the output is very dirty.  Then I
tied RA1 to +5 through a 5k resistor and all my problems went away,
RA0's output cleaned up.

In the book it says for lowest current consumption in sleep mode all I/O
pins should be at VDD or VSS.  I don't use sleep mode, but should I tie
all my unused pins to VDD or VSS?  Do I need the resistor if I tie them
to VDD?  Any other thoughts on what to do with unused pins?



1994\07\27@173253 by dpalmer

Are you sure that you are not trying to source to much out of the output
pin?  I sometimes only use the lower 2 pins on port A, because I try
to make port A always RS232 pins, and I have no problems at all.  
Try to put a pull-up resistor on the output pin and see if it works.
Check to make sure you are not trying to pulse the lines too fast, once
I tried to generate a 2 mhz clock from an output pin until I very
carefully figured out the capacitance in my 22 awg hook-up wire that was
7 inches long. :)

Darryl Palmer

1994\07\28@000401 by dthomas

That's easy.  Make all unused pins outputs.  Then you can let them
float.  Leaving inputs floating is definitely "considered harmful".


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