Folks,
I'm debugging a small circuit board with a PIC 18F4320 chip, using
MPLab 8.53 and a PICkit 3.  Everything works fine in both debug and
release modes on power-up IF the PICkit 3 is connected or reconnected.

I'm using an AC adapter as +5v supply and disconnect the cord at the
circuit board to power down.  Master Clear (inverted MCLR) is done by
a pushbutton microswitch to ground, with pin 1 of the PIC (!MCLR) also
connected through 10K ohms to +5v for pull-up (recommended config. by
the PICkit 3 docs).

1. If I power-up the bare board (i.e., with PICkit 3 disconnected) by
connecting the already powered-up adapter to the board, the PIC is in
a hung state.  Pressing and releasing the master clear pushbutton
doesn't do any good.

2. HOWEVER, if I reconnect the PICkit 3 connector, nothing happens,
but I get a dialog box on the PC warning me to make sure that I have
the right Vdd  voltage on the chip (a new feature of the PICkit 3,
which doesn't power the board under test like the PICkit 2),  When I
respond to the dialog box, the PICkit 3 pulses Pin 1 MCLR low and the
PIC starts up fine.

3. ALSO, if the PIC is under continuous power, the pushbutton master
clear switch works fine, i.e., the PIC goes back through its startup
code.

All of which seems to indicate that the master clear switch/circuit
works fine, i.e., pulls pin 1 to ground OK, but there's something
funky with the timing of the powerup sequence and/or switch-actuated
MCLR vs. PICkit-driven MCLR.

Should I condition the pushbutton signal or run it through a one-shot?

TIA,

Mike

PS: In the Config bits, I have the Power Up Timer enabled and am
running a 10 MHz crystal with HS-PLL mode, i.e., 40 MHz clock rate for
the PIC.
--=20
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist
.