At 06:12 PM 3/01/99 -0800, you wrote:

Dave,

Could it be RA4 which is an open collector??


good luck,


Peter Grey

>I discovered a problem with either my circuit or my PIC code, and I'm
>stumped. Not sure anyone can help "remotely", but on the off chance the
>symptoms ring any bells for anyone, I thought I'd write it up.
>
>One of my porta pins (this is a 16f84) is used to turn on and off power
>to an external device. porta has some input pins and some output pins,
>but none of them change from one to the other, so I don't think it's a
>"read-modify-write" problem.
>
>The pin is directly connected to the input of one gate of a 74HC14 (hex
>schmitt inverter), and the inverter in turn drives the gate of an
>n-channel MOSFET: so when the porta pin is high, the inverter output is
>low, turning the FET "on". And vice versa.
>
>I'm using bsf and bcf to toggle the pin. The problem is that the pin,
>once it's been brought high, doesn't seem to want to go back low. I
>assume it's a software problem, but I've been over the code many, many
>times and can't find it. And in fact the simulator tells me it's working
>fine: under simulation, the pin goes low when it should. But in the
>circuit, once it's on it stays on. Weird. I'm stumped.
>
>I can't for the life of me think of any electrical reason the pin should
>get stuck "on", can anyone else? I've tried several different PICs, and
>the symptoms are the same, so I don't think I blew up that pin. Besides,
>when I reset, it goes low, as it should at startup.
>
>Any ideas or debugging techniques that might be helpful will be greatly
>appreciated.
>
>Dave Johnson
>
>