Input H value?

arrow · Joined: 17 May 2005 Posts: 213

Hi

I am using the PIC16F873, and I have an input to PIN_B5. The input is the same as an output from another microcontroller (I dont know which one), and is connected to a R and an LED. This unknown uC is running on 3.2V. My PIC is running on 5V.

I would like to monitor when the LED controlled by the unknown uC turns ON. I am using:

epideath · Joined: 07 Jun 2006 Posts: 47

3.2V should be enough to input as a HIGH value. My PIC communicates to a 3.3v MMC without problems. PIC runs on 5V. There might be something else going on with your code or wiring.

Regards

Ttelmah · Guest

Agreed, it should work. Pin B5, has a TTL input buffer,which requires just 2v, to be seen as 'high', when running off a 5v supply. The 'odds' are that the output is not actually getting anywhere near the 3.3v level, because of the LED load, and this may be the problem. You need to check with a scope/meter, what voltage is actually arriving at the PIC. Remember the gounds need to be connected together as well, for this to work.

Best Wishes

kender · Joined: 09 Aug 2004 Posts: 768 Location: Silicon Valley

The LED, probably, has a resistor connected in series. Could it be that you are connectin the PIC to the resistor, instead of the actual pin on the uC?

arrow · Joined: 17 May 2005 Posts: 213

Hi

Thank you for all your replies.

Yes, I am connecting PIN_B5 to the Resistor and not the uC pin (is this important?).
I have also checked with an Oscope what comes in on PIN_B5
and it is 3.2V.

So I am not sure what I am doing wrong.

Once again thank you- and back to the debugging.
a.

kender · Joined: 09 Aug 2004 Posts: 768 Location: Silicon Valley