LDmicro Forum - PIC16F876 Pin 16 & 17 low voltage O/P

PIC16F876 Pin 16 & 17 low voltage O/P (by Jack)

Attached is a simple program that demonstrates a problem I am having. When I press button 4, 5 & 6 an LED should come on. They do but the LEDs connected to Pins 16 & 17 on the PIC16F876 are about extremely dull (look hard to see it is on) in comparison to the one connected to Pin 15 (& other pin on a bigger program). All the LEDs are connected to 330 ohm resistors and the 3 inputs are tied to 0V with a 10k resistor. I have checked the resistors and LEDs with a meter and they are fine.

I have check configuration bits but none appear to affect these 2 pins. I have a much more complicated program that I am running and this is the only problem I am having. The program simulate fine and the logic all works as it should but the LEDs are dull.

Any ideas? Is the SPI mode affecting these pins?

Fri Nov 27 2009, 22:21:40, download attachment IO Test.ld

(no subject) (by Jonathan Westhues)

That's a little odd.

What power supply voltage are you running from? And can you measure the voltage across the 330 ohm resistor, and the voltage at the pin, for both the bright and dim LEDs?

It would be better to do that with an oscilloscope, but a digital voltmeter is okay too.

Fri Nov 27 2009, 22:41:39

(no subject) (by David R)

Hi,
I have never had this kind of problem with this chip.
Could it be any thing to do with the first letter of the word
"Test" being A capital letter as I as I am sure I read somewhere they cant.
Regards
David.

Sat Nov 28 2009, 16:24:18

(no subject) (by Jack)

Sorry guys. It has taken a while before I could get back to this. It was a short in the PCB that caused the LEDs to not operate. The short was between the 330 ohm resistors making the dropping resistor to be 165 ohms. I would have thought the OP would try to turn on but it didn't (no flicker). When testing externally the power supply had no problems driving through the resistors. Always learning and thank you for your feed back. Hopefully I don't waste your time with silly things like this again.

Cheers.

Tue Dec 8 2009, 05:30:18