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
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