Post by thread:unused data lines on pic16c5x

Hi, 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? Thanx, mycal

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

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