Electronics > Beginners
PIC I/O port affecting adjacent I/O port - why?
bpb:
Hi,
I am new to electronics and am seeing something I don't understand when trying to visualize I/O ports on a PIC microcontroller (PIC16F690).
The probe on the left side of the img is connected to a PORTC I/O pin, and the probe at the bottom of the img is *not* a PORTC I/O pin (but is adjacent to one).
When setting PORTC pins to logic one, I see the expected ~5V on the PORTC pin and ~0V on the adjacent pin:
However, when toggling the PORTC pins, it affects the adjacent pin! What?? How??
dom0:
The other pin is configured as an input without pull-up, i.e. High-Z? In that case it is capacitive feedthrough to the other pin.
bpb:
--- Quote from: dom0 on November 09, 2019, 03:09:49 pm ---The other pin is configured as an input without pull-up, i.e. High-Z? In that case it is capacitive feedthrough to the other pin.
--- End quote ---
Here's a shot with the adjacent pin configured as an output port set to logic 0. Is this still "capacitive feedthrough"?
rstofer:
I don't see any decoupling capacitors on the Vcc/Gnd pins. That's a really big deal when things happen fast - like rising/falling edges.
dom0:
That's ringing due to the inductiveness of the ground leads of your probes and the power supply lines. Usually it looks quite a bit worse than this with a setup like you showed in the picture.
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