16f887 PIC output pin pull to ground

[bodgetts]

I managed to get it working, it turns out the specs on the board were not very clear. I could connect the output pins of my PIC directly to the signal and set them low. I thought that maybe I would have to do something tricky, but was dead simple.

Thanks for the help guys.

[kenif]

In the old days a TTL low was not very low, it only had to be below 800mv.
So an older device (say 74LS04) would give a low of one junction above ground, around 600mv.
These days most devices (like PICs or 74HCT04) are CMOS, so a low is no longer one bipolar junction voltage above ground, but an impedance above ground.
The difference is that now the output behaves more like a resistor to ground (an FET), and the value of the low is a function of the current it's sinking, which means it's typically very, very low. Or, if you prefer to round these numbers down: ground.

[bodgetts]

Ok, I understand now. Thanks kenif!

[Sneaky-geek]

Hello All,
Without seeing a complete schematic:
Be careful as to how much current you are trying to sink!
Please place a 330 ohm 1/2 watt resistor this limits the current that the pic output is switching to 15 ma. Or use a 200 ohm 1/2 watt to limit current to 25 ma, the MAXIMUM that the pin is rated for.

Just a thought,

Terry K9HA