You have hit nail on the head re: no Voh, Ioh curves.
I'm running off two AAA batteries, so fresh batteries give me about 3V, but mid life, it may be as low as 2.7V
I have a Blue LED with a voltage drop of 2.7V @ 10mA so I was planning on a choosing a series resistor for a dependable 7 mA.
For one reason or another I chose a 22 Ohm resistor, expecting more than enough current with fresh batteries.
What I ended up with was 2.67V out of the port pin, 2.6V across the LED, and only 3.3 mA through the LED.
Other non-loaded output pins were running at 2.96V
So, I figured I must be pulling more current than expected from the output pin.
At this point the thought did occur to me that perhaps I should have used the port pin as a current sink, instead of a source, but I mistakenly thought that only mattered on TTL logic.
So, this is when I started delving into the spec sheet to determine what currents I should have expected without significant output voltage drops. And I came up with zip....
Note: I also have a 1.9V RED LED on an output, with a 100 ohm resistor I get 5mA current with 2.4V on the output pin.
It would be really nice to have an actual spec for these outputs so I could know what to expect. Even if it was a generic electrical spec for the family of devices.
My only clue is that the output H voltage drop is specified at 0.7V at 3mA where as the Output Low voltage is specified at 0.6V at 6mA. So, clearly it sinks current better than it sources it.
It also begs the question, do I even need a current limit resistor with green and blue LEDs.
So I think I've done my due diligence....
Does anyone have an actual chart showing how these outputs are meant to perform?
post edited by Philbot - 2019/07/27 18:02:49