> I'm fairly new to PIC development and am just trying some things out
> right now. I want to get my PC and PIC talking over a serial port and
> am having trouble figuring some things out. It's a 16F84A.
>
> I'm using a DB-9 connector from my PC to the PIC, with the TX and RX
> pins connected to I/O pins on my PIC. What I'm having trouble with is
> pin 5 on the DB-9, which is apparently should go to ground.
>
> If I have pin 5 connected to the same ground as my PIC, the PIC will
> not start. I have a serial LCD hooked up for debugging, and nothing
> appears. If I disconnect pin 5, the PIC will start up just fine and
> display my debugging output.
>
> My test program is also supposed to send text to the PC via the serial
> port. If the serial ground pin is not connected, and the PIC starts,
> nothing is received by the PC. If I connect the serial ground to the
> PIC ground after it has started, one of the following happens: the PC
> will receiving data just fine, the PIC will reset, or the PIC will
> just stop doing anything.
>
> I'm confused on what I should be doing with the ground pin on the
> serial port. Should it be on the same ground as the PIC? If I connect
> my multimeter to pin 5, then to the PIC ground, I see it's putting out
> 9V. Does that seem normal? It seems like I probably shouldn't be
> connecting 9V to the same ground line that the PIC connects to, but I
> don't know for sure.
>
> Thanks!
>
> --
> Ben Sinclair
> ben@bensinclair.com
> --
Yes, pin 5 should be connected to the ground of your PIC
circuit. You should not be seeing 9 volts. Stop what you are
doing until you figure out the problem. A 16F84A is a pretty
hearty chip but 9 volts to ground is definately not good.

Can you describe your PIC circuit ?
Do you have a scope or logic analyzer to troubleshoot with ?
Are you sure the DB9 connector is correct ?  Did you make it
or buy it ?

~Kevin

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