Uno to Nano IO

Hello,

Been having a bit of trouble getting the output from one controllers IO to the other to be detected and was wondering if anyone was able to explain why?

I'm using an Uno to send a PWM signal to the Nano, but unless I put a resistor between the input pin and Ground, the input pin voltage doesn't swing to 0v.

Any ideas?

Thanks

Should probably also mention it doesn’t seem to matter if it’s PWM output or not. A stable HIGH output still needs the resistor for some reason?

Nevermind, found out what the issue was. Turns out I had the DDRD register inverted so what I thought was an output was actually a PULLUP INPUT. Doh! :-*

I often thought 1 should have been input and 0 should have been output. :wink:

.

Haha, yeah, it's a bugger when your doing port manipulation :stuck_out_tongue: